merge-trees: push choice to renormalize away from low level

merge-trees: push choice to renormalize away from low level

The merge machinery decides whether to resmudge and clean relevant
entries based on the global merge_renormalize setting, which is set by
"git merge" based on its configuration (and left alone by other
commands).

A nicer interface would make that decision a parameter to merge_trees
so callers would pass in a choice made on a call-by-call basis.
Start by making blob_unchanged stop examining the merge_renormalize
global.

In other words, this change is a trivial no-op, but it brings us
closer to something good.

Cc: Eyvind Bernhardsen <eyvind.bernhardsen@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>