bash: teach __git_ps1 about CHERRY_PICK_HEAD

Make the git prompt (when enabled) show a CHERRY-PICKING indicator
when we are in the middle of a conflicted cherry-pick, analogous
to the existing MERGING and BISECTING flags.

Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -246,6 +246,8 @@ __git_ps1 ()
 				fi
 			elif [ -f "$g/MERGE_HEAD" ]; then
 				r="|MERGING"
+			elif [ -f "$g/CHERRY_PICK_HEAD" ]; then
+				r="|CHERRY-PICKING"
 			elif [ -f "$g/BISECT_LOG" ]; then
 				r="|BISECTING"
 			fi