fsmonitor: use vfs instead of opener (issue5938)

"opener" of localrepository object was dropped at Mercurial 4.3 (or
a7e210167c28). "vfs" should be used instead.

wlock is required to write into a file under .hg directory.

For efficiency, we should change _cmpsets() from:

  1. acquire wlock
  2. open log file under .hg directory with write mode
  3. compare between result of watchman and Mercurial's dirstate logic
  4. write out error info into a file, if error is detected
  5. release wlock

to:

  1. compare between result of watchman and Mercurial's dirstate logic
  2. acquire wlock, if error is detected
  3. open and write error info into a file
  4. release wlock

But this is another issue.

hgext/fsmonitor/__init__.py

@@ -460,7 +460,7 b' def overridestatus('
                 f = open(fn, 'wb')
             else:
                 fn = 'fsmonitorfail.log'
-                f = self.opener(fn, 'wb')
+                f = self.vfs.open(fn, 'wb')
         except (IOError, OSError):
             self.ui.warn(_('warning: unable to write to %s\n') % fn)
             return
@@ -564,7 +564,9 b' def overridestatus('
             self.ui.fout, self.ui.ferr = fout, ferr
 
         # clean isn't tested since it's set to True above
-        _cmpsets([modified, added, removed, deleted, unknown, ignored, clean],
+        with self.wlock():
+            _cmpsets(
+                [modified, added, removed, deleted, unknown, ignored, clean],
                  rv2)
         modified, added, removed, deleted, unknown, ignored, clean = rv2