Merge branch 'sz/submodule-force-update'

"git submodule update --force" used to leave the working tree of the
submodule intact when there were local changes.  It is more intiutive
to make "--force" a sign to run "checkout -f" to overwrite them.

* sz/submodule-force-update:
  Make 'git submodule update --force' always check out submodules.

git-submodule.sh

@@ -603,7 +603,7 @@ Maybe you want to use 'update --init'?")"
 			die "$(eval_gettext "Unable to find current revision in submodule path '\$sm_path'")"
 		fi
 
-		if test "$subsha1" != "$sha1"
+		if test "$subsha1" != "$sha1" -o -n "$force"
 		then
 			subforce=$force
 			# If we don't already have a -f flag and the submodule has never been checked out