add status config and command line options for rename detection

add status config and command line options for rename detection

After performing a merge that has conflicts git status will, by default,
attempt to detect renames which causes many objects to be examined.  In a
virtualized repo, those objects do not exist locally so the rename logic
triggers them to be fetched from the server. This results in the status call
taking hours to complete on very large repos vs seconds with this patch.

Add a new config status.renames setting to enable turning off rename
detection during status and commit.  This setting will default to the value
of diff.renames.

Add a new config status.renamelimit setting to to enable bounding the time
spent finding out inexact renames during status and commit.  This setting
will default to the value of diff.renamelimit.

Add --no-renames command line option to status that enables overriding the
config setting from the command line. Add --find-renames[=<n>] command line
option to status that enables detecting renames and optionally setting the
similarity index.

Reviewed-by: Elijah Newren <newren@gmail.com>
Original-Patch-by: Alejandro Pauly <alpauly@microsoft.com>
Signed-off-by: Ben Peart <Ben.Peart@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>