git-add: remove conflicting entry when adding.

When replacing an existing file A with a directory A that has a
file A/B in it in the index, 'git add' did not succeed because
it forgot to pass the allow-replace flag to add_cache_entry().

It might be safer to leave this as an error and require the user
to explicitly remove the existing A first before adding A/B
since it is an unusual case, but doing that automatically is
much easier to use.

Signed-off-by: Junio C Hamano <junkio@cox.net>

read-cache.c

diff --git a/read-cache.c b/read-cache.c
index a602010..983e68b 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -358,7 +358,7 @@
 
 	if (index_path(ce->sha1, path, &st, 1))
 		die("unable to index file %s", path);
-	if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD))
+	if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE))
 		die("unable to add %s to index",path);
 	if (verbose)
 		printf("add '%s'\n", path);