git-gui: remove .git/CHERRY_PICK_HEAD after committing

Adding _git_ps1() to one's bash prompt displays various repo status
info after each command. After committing a git cherry-pick -n using
git-gui, the prompt still contains the "|CHERRY-PICKING" flag.

Delete the file causing this flag when cleaning up.

Signed-off-by: Beat Bolli <bbolli@ewanet.ch>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>

lib/commit.tcl

@@ -409,6 +409,7 @@ A rescan will be automatically started now.
 	catch {file delete [gitdir MERGE_MSG]}
 	catch {file delete [gitdir SQUASH_MSG]}
 	catch {file delete [gitdir GITGUI_MSG]}
+	catch {file delete [gitdir CHERRY_PICK_HEAD]}
 
 	# -- Let rerere do its thing.
 	#