cvs: skip bad tags

If the CVS repo somehow has a symbolic name that references a revision
consisting of a single number (e.g. BAD_TAG: 1), convert will fail when
attempting to find the branches, preventing the initial import from
working.
This patch skips those symbolic names--without warning.

hgext/convert/cvsps.py

@@ -402,6 +402,8 b' def createlog(ui, directory=None, root="'
             branchpoints = set()
             for branch, revision in branchmap.iteritems():
                 revparts = tuple([int(i) for i in revision.split('.')])
+                if len(revparts) < 2: # bad tags
+                    continue
                 if revparts[-2] == 0 and revparts[-1] % 2 == 0:
                     # normal branch
                     if revparts[:-2] == e.revision: