git add --intent-to-add: fix removal of cached emptiness

This uses the extended index flag mechanism introduced earlier to mark
the entries added to the index via "git add -N" with CE_INTENT_TO_ADD.

The logic to detect an "intent to add" entry for the purpose of allowing
"git rm --cached $path" is tightened to check not just for a staged empty
blob, but with the CE_INTENT_TO_ADD bit.  This protects an empty blob that
was explicitly added and then modified in the work tree from being dropped
with this sequence:

	$ >empty
	$ git add empty
	$ echo "non empty" >empty
	$ git rm --cached empty

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/cache.h b/cache.h
index ef2e7f93f..f15b3fc90 100644
--- a/cache.h
+++ b/cache.h
@@ -176,10 +176,11 @@ struct cache_entry {
 /*
  * Extended on-disk flags
  */
+#define CE_INTENT_TO_ADD 0x20000000
 /* CE_EXTENDED2 is for future extension */
 #define CE_EXTENDED2 0x80000000
 
-#define CE_EXTENDED_FLAGS (0)
+#define CE_EXTENDED_FLAGS (CE_INTENT_TO_ADD)
 
 /*
  * Safeguard to avoid saving wrong flags: