Merge branch 'rr/minimal-stat'

Some reimplementations of Git does not write all the stat info back
to the index due to their implementation limitations (e.g. jgit
running on Java).  A configuration option can tell Git to ignore
changes to most of the stat fields and only pay attention to mtime
and size, which these implementations can reliably update.  This
avoids excessive revalidation of contents.

* rr/minimal-stat:
  Enable minimal stat checking

diff --cc cache.h
Simple merge