Don't hardcode ~/git/oil in the Makefile.

Addresses issue #21.

Makefile

@@ -166,6 +166,15 @@ _build/hello/bytecode.zip: $(HELLO_SRCS) \
_build/oil/main_name.c:
	$(ACTIONS_SH) main-name bin.oil oil.ovm > $@

# The root of this repo, e.g. ~/git/oil, should be our PYTHONPATH for
# detecting dependencies.
# 
# From this link:
# https://stackoverflow.com/questions/322936/common-gnu-makefile-directory-path
# Except we're using 'firstword' instead of 'lastword', because
# _build/oil/ovm.d is the last one.
REPO_ROOT := $(abspath $(dir $(firstword $(MAKEFILE_LIST))))

# Dependencies calculated by importing main.
# NOTE: The list of files is used both to compile and to make a tarball.
# - For compiling, we should respect _HAVE_READLINE in detected_config
@@ -175,7 +184,7 @@ _build/oil/main_name.c:
# package.  build/doc.sh currently makes _build/__init__.py.
_build/oil/app-deps-%.txt: _build/detected-config.sh build/app_deps.py
	test -d _build/oil && \
	  $(ACTIONS_SH) app-deps oil ~/git/oil bin.oil
	  $(ACTIONS_SH) app-deps oil $(REPO_ROOT) bin.oil

_build/osh_help.py: doc/osh-quick-ref-pages.txt
	build/doc.sh osh-quick-ref