"needs update" considered harmful

"needs update" considered harmful

"git update-index --refresh", "git reset" and "git add --refresh" have
reported paths that have local modifications as "needs update" since the
beginning of git.

Although this is logically correct in that you need to update the index at
that path before you can commit that change, it is now becoming more and
more clear, especially with the continuous push for user friendliness
since 1.5.0 series, that the message is suboptimal.  After all, the change
may be something the user might want to get rid of, and "updating" would
be absolutely a wrong thing to do if that is the case.

I prepared two alternatives to solve this.  Both aim to reword the message
to more neutral "locally modified".

This patch is a more intrusive variant that changes the message for only
Porcelain commands ("add" and "reset") while keeping the plumbing
"update-index" intact.

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