build-sys: Include the .version file in the distribution tarball

As per the comments in git-version-gen, the .version file that is
typically generated automatically during build should be included
in the tarball, so generate it in the dist-hook.

This fixes a problem when running make distcheck which uses a read-only
source folder and thus cannot generate the $top_srcdir/.version as
part of it's build process (it uses a _build folder which is r/w)
and thus cannot be built.

Makefile.am

@@ -77,6 +77,7 @@ dist-hook:
 		( git-changelog.perl || echo "git-changelog.perl failed." ) > ${distdir}/ChangeLog 2>&1 ; \
 	fi
 	echo $(VERSION) > $(distdir)/.tarball-version
+	echo $(VERSION) > $(distdir)/.version
 
 .PHONY: homepage distcleancheck doxygen
 

git-version-gen

@@ -67,6 +67,7 @@ scriptversion=2008-04-08.07.01
 #	echo $(VERSION) > $@-t && mv $@-t $@
 # dist-hook:
 #	echo $(VERSION) > $(distdir)/.tarball-version
+#	echo $(VERSION) > $(distdir)/.version
 
 case $# in
     1) ;;