git-cherry-pick: add allow-empty option

git cherry-pick fails when picking a non-ff commit that is empty.  The advice
given with the failure is that a git-commit --allow-empty should be issued to
explicitly add the empty commit during the cherry pick.  This option allows a
user to specify before hand that they want to keep the empty commit.  This
eliminates the need to issue both a cherry pick and a commit operation.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/sequencer.h b/sequencer.h
index bb4b138..e2cd725 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -29,6 +29,7 @@
 	int signoff;
 	int allow_ff;
 	int allow_rerere_auto;
+	int allow_empty;
 
 	int mainline;