Rename internal function "add_file_to_cache" in builtin-update-index.c
Rename internal function "add_file_to_cache" in builtin-update-index.c

I'd like to consistently name all index-layer functions that
operate on the default index xxx_cache(), and this application
specific function interferes with the plan.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git