fakemergerecord: take wlock to write the merge state

The merge state is supposed to be covered by the wlock. We fix the test
extensions to comply to that.

tests/fakemergerecord.py

@@ -16,10 +16,11 b' command = cmdutil.command(cmdtable)'
          [('X', 'mandatory', None, 'add a fake mandatory record'),
           ('x', 'advisory', None, 'add a fake advisory record')], '')
 def fakemergerecord(ui, repo, *pats, **opts):
-    ms = merge.mergestate.read(repo)
-    records = ms._makerecords()
-    if opts.get('mandatory'):
-        records.append(('X', 'mandatory record'))
-    if opts.get('advisory'):
-        records.append(('x', 'advisory record'))
-    ms._writerecords(records)
+    with repo.wlock():
+        ms = merge.mergestate.read(repo)
+        records = ms._makerecords()
+        if opts.get('mandatory'):
+            records.append(('X', 'mandatory record'))
+        if opts.get('advisory'):
+            records.append(('x', 'advisory record'))
+        ms._writerecords(records)