Update build system (automake, autoconf, libtool)

Unfortunately this patch is hard to split up into smaller chunks. Our build
system and the associated automake/autoconf/libtool macros has been left
untouched for a while, and could use a refresher.

* Upgrade ltmain.sh to the latest version
* Move away from a huge acinclude.m4 directory to using individual files in
  the m4/ subdirectory, suggested by upstream automake documentation
* Update all macros to their latest available version
* Adjust Makefile.am and autogen.sh to accommodate m4/ subdirectory

Signed-off-by: Dan McGee <dan@archlinux.org>

Makefile.am

@@ -3,6 +3,8 @@ if WANT_DOC
 SUBDIRS += doc
 endif
 
+ACLOCAL_AMFLAGS = -I m4 --install
+
 # Make sure we test and build manpages when doing distcheck
 DISTCHECK_CONFIGURE_FLAGS = --enable-doc --disable-git-version