branchcache: stay silent if failing to read cache files

The warning has in some cases incorrectly attributed unrelated problems to rbc.

Instead, just do like the branch head cache does and stay quiet when reading
fails. The cache will be missing the first time a repo is used. It is a normal
situation and there is no reason to make a note of that.

mercurial/branchmap.py

@@ -316,8 +316,6 b' class revbranchcache(object):'
             self._rbcsnameslen = len(bndata) # for verification before writing
             self._names = [encoding.tolocal(bn) for bn in bndata.split('\0')]
         except (IOError, OSError), inst:
-            repo.ui.debug("couldn't read revision branch cache names: %s\n" %
-                          inst)
             if readonly:
                 # don't try to use cache - fall back to the slow path
                 self.branchinfo = self._branchinfo

tests/test-casefolding.t

@@ -28,7 +28,6 b' test case collision on rename (issue750)'
   a
   committing manifest
   committing changelog
-  couldn't read revision branch cache names: * (glob)
   committed changeset 0:07f4944404050f47db2e5c5071e0e84e7a27bba9
 
 Case-changing renames should work:

tests/test-convert-svn-encoding.t

@@ -53,7 +53,6 b' Convert while testing all possible outpu'
   source: svn:afeb9c47-92ff-4c0c-9f72-e1f6eb8ac9af/trunk@1
   converting: 0/6 revisions (0.00%)
   committing changelog
-  couldn't read revision branch cache names: * (glob)
   4 hello
   source: svn:afeb9c47-92ff-4c0c-9f72-e1f6eb8ac9af/trunk@2
   converting: 1/6 revisions (16.67%)