valac: don't append -dirty to version

Don't append -dirty to the valac version number if the Buildroot Git
tree has uncommited changes.

The patched script is meant for the valac developers, but it also
activates if you build valac in a subdirectory of a Git tree (e.g.
as is commonly done in Buildroot).

The effect is that valac gets built as being version x.y.z-dirty, which
breaks programs (such as Midori) that explicitly check for valac-x.y.z.

Signed-off-by: Simon Dawson <spdawson@gmail.com>
diff -Nur a/build-aux/git-version-gen b/build-aux/git-version-gen
--- a/build-aux/git-version-gen	2010-08-15 12:49:03.000000000 +0100
+++ b/build-aux/git-version-gen	2012-05-14 10:17:19.977204570 +0100
@@ -135,7 +135,7 @@
     *) # Append the suffix only if there isn't one already.
 	case $v in
 	  *-dirty) ;;
-	  *) v="$v-dirty" ;;
+	  #*) v="$v-dirty" ;;
 	esac ;;
 esac