access "native-pkgs" as a git submodule

This looks like a good use case for submodules, because the
native-library packages change infrequently, and no one cares
about the history of changes relative to the rest of the
project (except to be able to get a set of packages that is
consistent with the rest of the repository).

The change avoids the problem that `make' on Mac OS X would
try a `git update', which is no good if you happen to be
offline (and have your "buidl.native-pkgs" repo pull from the
obvious place).

Finally, it's easier for Windows users, since `git submodule init'
and `git submodule update' is easier to use and remember than
`git clone <some-repository-URL>'. The makefile more helpfully
complains if "native-pkgs" doesn't seem to have been initialized
as a submodule.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "native-pkgs"]
+	path = native-pkgs
+	url = https://github.com/plt/libs.git

INSTALL.txt

@@ -18,14 +18,17 @@ The "pkgs" directory contains the packages that are included in a
 Racket distribution, plus some additional packages (such as tests).
 
 On Unix and Mac OS X, you can build Racket plus the included packages
-with `make in-place' (or just `make'). The resulting build is in the
-"racket" subdirectory. For now, you need to have `git' installed for
-downloading native-library packages. If you want more control over the
-process, see below.
-
-On Windows, you must first clone "git://github.com/plt/libs.git"
-as "build/native-pkgs". Then, you can use `nmake win32-in-place',
-as long as you're using Microsoft Visual Studio 9.0 (2008).
+with `make in-place' (or just `make'). On Windows, you can use `nmake
+win32-in-place', as long as you're using Microsoft Visual Studio 9.0
+(2008). The resulting build is in the "racket" subdirectory. If you
+want more control over the process, see below.
+
+On Mac OS X and Windows, you'll need native-library packages in the
+"native-pkgs" directory. In the git repostory, "native-pkgs" is a git
+submodule, so you'll need
+   git submodule init
+   git submodule update
+to get it set up.
 
 To install a subset of the packages in "pkgs", supply `PKGS' value to
 `make'. For example,
@@ -123,16 +126,9 @@ scope. Packages are linked with the `--no-setup' flag (effectively),
 which means that a `raco setup' is needed after installing links.
 
 Native-library packages provide (on Mac OS X and Windows) pre-built
-native libraries, such as Cairo. Currently, the libraries must be
-downloaded from GitHub. On a non-Windows platform, the
-`native-from-git' makefile target clones/updates the native-library
-repository from GitHub; otherwise, clone
-
-   git://github.com/plt/libs.git
-
-as
-
-   build/native-pkgs
+native libraries, such as Cairo. They are available through a git
+submodule "native-pkgs", so use `git submodule init' and `git
+submodule update' as needed.
 
 By default, the `PKGS' value is remembered by `pkg-links', but a
 previously remembered value is not used. Supply `LINK_MODE=--restore'
@@ -160,10 +156,8 @@ looks like to install individual packages as if provided by a server
 (i.e., not through development-mode links).
 
 Use `make local-catalog' to create a package catalog that provides
-mappings for all of the packages in "pkgs" as well as packages
-pre-built native libraries downloaded from GitHub. (On Unix, use the
-`local-source-catalog' makefile target to skip native libraries, since
-none are needed.)
+mappings for all of the packages in "pkgs" as well as packages for
+pre-built native libraries.
 
 To install a package, try
 
@@ -374,10 +368,9 @@ In more detail:
 
      The `SRC_CATALOG' variable determines the catalog that is used to
      get package sources and native-library packages, but a value of
-     "local" triggers a bootstrap mode where native libraries are
-     downloaded directly from GitHub and all other packages are
-     represented by directories in the makefile's directory. For now,
-     "local" is the default.
+     "local" triggers a bootstrap mode where packages are represented
+     by directories in the makefile's directory. For now, "local" is
+     the default.
 
      The server provides README files from the "build/readmes"
      directory. If "README.txt" does not exist when the sever is

Makefile

@@ -202,12 +202,13 @@ BUNDLE_CONFIG = bundle/racket/etc/config.rktd
 # ------------------------------------------------------------
 # Linking all packages (development mode; not an installer build)
 
-LINK_ALL = -U -G build/config racket/src/link-all.rkt ++dir pkgs ++dir build/native-pkgs
+LINK_ALL = -U -G build/config racket/src/link-all.rkt ++dir pkgs ++dir native-pkgs
 
 pkg-links:
 	$(PLAIN_RACKET) $(LINK_ALL) $(LINK_MODE) $(PKGS) $(REQUIRED_PKGS)
 
 win32-pkg-links:
+	IF NOT EXIST native-pkgs\racket-win32-i386 $(MAKE) complain-no-submodule
 	$(MAKE) pkg-links PLAIN_RACKET="$(WIN32_PLAIN_RACKET)" LINK_MODE="$(LINK_MODE)" PKGS="$(PKGS)"
 
 # ------------------------------------------------------------
@@ -250,9 +251,12 @@ local-catalog:
 
 # Get pre-built native libraries from the repo:
 native-from-git:
-	mkdir -p build
-	if [ ! -d build/native-pkgs ]; then cd build; git clone git://github.com/plt/libs.git native-pkgs ; fi
-	cd build/native-pkgs; if [ -d ".git" ]; then git pull ; fi
+	if [ ! -d native-pkgs/racket-win32-i386 ]; then $(MAKE) complain-no-submodule ; fi
+complain-no-submodule:
+	: Native packages are not in the expected subdirectory. Probably,
+	: you need to use 'git submodule init' and 'git submodule update' to get
+	: the submodule for native packages.
+	exit 1
 
 # Create packages and a catalog for all native libraries:
 native-catalog: