git-gui: Describe deleted symlinks in a more friendly way.

Currently core-git's diff utilities report a deleted symlink as a
deleted file with a mode of 120000.  This is not nearly as user
friendly as one might like, as the user must remember that 120000
is the UNIX mode bits for a symlink.  So instead we transform
the not-so-friendly message from core-git into a slightly more
user friendly "deleted symlink" message.

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

git-gui

@@ -628,6 +628,9 @@ proc read_diff {fd} {
 		if {[string match {diff --combined *} $line]} continue
 		if {[string match {--- *} $line]} continue
 		if {[string match {+++ *} $line]} continue
+		if {$line eq {deleted file mode 120000}} {
+			set line "deleted symlink"
+		}
 		if {[string match index* $line]} {
 			if {[string first , $line] >= 0} {
 				set diff_3way 1