localrepo: allow wlock to be inherited

This is part of a series that will allow locks to be inherited by subprocesses
in limited circumstances.

When allowed, the parent process will pass down requisite information to the
child process by way of this environment variable.

mercurial/localrepo.py

@@ -1296,7 +1296,7 b' class localrepository(object):'
 
         l = self._lock(self.vfs, "wlock", wait, unlock,
                        self.invalidatedirstate, _('working directory of %s') %
-                       self.origroot)
+                       self.origroot, parentenvvar='HG_WLOCK_LOCKER')
         self._wlockref = weakref.ref(l)
         return l
 

tests/test-fncache.t

@@ -205,7 +205,7 b' Aborting lock does not prevent fncache w'
   > from mercurial import commands, util
   > from mercurial.extensions import wrapfunction
   > 
-  > def lockexception(orig, vfs, lockname, wait, releasefn, acquirefn, desc):
+  > def lockexception(orig, vfs, lockname, wait, releasefn, acquirefn, desc, parentenvvar=None):
   >     def releasewrap():
   >         raise util.Abort("forced lock failure")
   >     return orig(vfs, lockname, wait, releasewrap, acquirefn, desc)