git-gui: Trim trailing slashes from untracked submodule names

Oddly enough `git ls-files --others` supplies us the name of an
untracked submodule by including the trailing slash but that
same git version will not accept the name with a trailing slash
through `git update-index --stdin`.  Stripping off that final
slash character before loading it into our file lists allows
git-gui to stage changes to submodules just like any other file.

This change should give git-gui users some basic submodule support,
but it is strictly at the plumbing level as we do not actually know
about calling the git-submodule porcelain that is a recent addition
to git 1.5.3.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -1010,7 +1010,11 @@ proc read_ls_others {fd after} {
 	set pck [split $buf_rlo "\0"]
 	set buf_rlo [lindex $pck end]
 	foreach p [lrange $pck 0 end-1] {
-		merge_state [encoding convertfrom $p] ?O
+		set p [encoding convertfrom $p]
+		if {[string index $p end] eq {/}} {
+			set p [string range $p 0 end-1]
+		}
+		merge_state $p ?O
 	}
 	rescan_done $fd buf_rlo $after
 }