Update INSTALL in the configure script.

The way we were building the INSTALL instructions was causing `make
distcheck` to fail: `make clean` wasn't cleaning up the INSTALL file, which
was what we wanted for building in the source directory, but not when
building from another directory.

Letting autoconf handle the INSTALL file fixes this problem, and simplifies
the Makefile in the process.

CONTRIBUTING.md

@@ -76,10 +76,8 @@ gitsh is packaged and installed using GNU autotools.
         ./autogen.sh
         ./configure
 
-3. Regenerate the installation instructions:
-
-        make INSTALL
-        git commit -m "Update INSTALL"-- INSTALL
+3. Commit your changes to `configure.ac`, `INSTALL`, and any other files that
+   were modified by the version bump.
 
 4. Build and publish the release:
 

Makefile.am

@@ -1,6 +1,6 @@
 AUTOMAKE_OPTIONS = foreign
 SUBDIRS = src man lib/gitsh vendor spec
-EXTRA_DIST = LICENSE README.md INSTALL.in
+EXTRA_DIST = LICENSE README.md INSTALL
 
 .PHONY: release \
 	release_build release_push release_clean \
@@ -14,9 +14,6 @@ edit_package = sed \
 	-e 's|@DIST_ARCHIVES[@]|$(DIST_ARCHIVES)|g' \
 	-e 's|@DIST_SHA[@]|$(DIST_SHA)|g'
 
-INSTALL: Makefile INSTALL.in
-	$(edit_package) $@.in > $@
-
 release: release_build release_push release_clean
 
 release_build: release_build_tarball release_build_homebrew release_build_arch

configure.ac

@@ -49,5 +49,5 @@ AC_SUBST([vendorfiles])
 AC_SUBST([testfiles])
 AC_SUBST([gemsetuppath])
 
-AC_CONFIG_FILES([Makefile src/Makefile lib/gitsh/Makefile man/Makefile vendor/Makefile spec/Makefile])
+AC_CONFIG_FILES([Makefile src/Makefile lib/gitsh/Makefile man/Makefile vendor/Makefile spec/Makefile INSTALL])
 AC_OUTPUT