localrepo: warn if we are writing to cache without a lock
From quite sometime we have two types of cache, `cache` and `wcache`. The later
one is a working copy cache and the first one is a store cache.
Let's add a check for warning if we are missing store lock while writing to
these caches.
This is inspired from some tag cache breakage which is observed when multiple
shares are in play.
The interesting part is that although we are still taking wlock to write store
caches at many places, but still the test pases.
Differential Revision: https://phab.mercurial-scm.org/D9000