git-gui: Prefer version file over git-describe.

Some distributions are using Git for part of their package
management system, but unpack Git's own source code for
delivery from the .tar.gz.  This means that when we walk
up the directory tree with git-describe to locate a Git
repository, the repository we find is for the distribution
and *not* for git-gui.  Consequently any tag we might find
there is bogus and does not apply to us.

In this case the version file should always exist and be
readable, as the packager is working from the released
.tar.gz sources.  So we should always favor the version
file over anything git-describe guess for us.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

GIT-VERSION-GEN

@@ -20,6 +20,11 @@ tree_search ()
 	done
 }
 
+# Always use the tarball version file if found, just
+# in case we are somehow contained in a larger git
+# repository that doesn't actually track our state.
+# (At least one package manager is doing this.)
+#
 # We may be a subproject, so try looking for the merge
 # commit that supplied this directory content if we are
 # not at the toplevel.  We probably will always be the
@@ -27,10 +32,13 @@ tree_search ()
 # that fact.
 #
 # If we are at the toplevel or the merge assumption fails
-# try looking for a gitgui-* tag, or fallback onto the
-# distributed version file.
+# try looking for a gitgui-* tag.
 
-if prefix="$(git rev-parse --show-prefix 2>/dev/null)"
+if test -f version &&
+   VN=$(cat version)
+then
+	: happy
+elif prefix="$(git rev-parse --show-prefix 2>/dev/null)"
    test -n "$prefix" &&
    head=$(git rev-list --max-count=1 HEAD -- . 2>/dev/null) &&
    tree=$(git rev-parse --verify "HEAD:$prefix" 2>/dev/null) &&
@@ -48,9 +56,6 @@ elif VN=$(git describe --abbrev=4 HEAD 2>/dev/null) &&
    esac
 then
 	VN=$(echo "$VN" | sed -e 's/^gitgui-//;s/-/./g');
-elif test -f version
-then
-	VN=$(cat version) || VN="$DEF_VER"
 else
 	VN="$DEF_VER"
 fi