revlog: always process opener options

I'm not sure when ``opener.options`` would ever be explicitly
set to None. It is definitely not possible to construct a repo
this way because ``localrepo.resolvestorevfsoptions()`` always
returns a dict and ``localrepo.makelocalrepository()`` always
sets ``opener.options`` to this value.

Because we always execute this code now, if options are empty
we defaulted to creating version 0 revlogs. So we had to change
the code slightly to fall back to the default revlog version
and flags.

As astute reader will note that it is not possible to create
version 0 revlogs now. However, I don't think it was possible
before, as this required ``opener.options`` being unset, which
I don't think was possible. I suspect this means our test
coverage for version 0 revlog repositories is possibly
non-existent! Since I don't see a config option to disable
revlog v1, I'm not even sure if we had a way to create new
repos with version 0 revlogs! Who knows.

Differential Revision: https://phab.mercurial-scm.org/D5559

mercurial/revlog.py

@@ -384,17 +384,18 class revlog(object):
         self._writinghandles = None
 
         mmapindexthreshold = None
-        v = REVLOG_DEFAULT_VERSION
-        opts = getattr(opener, 'options', None)
-        if opts is not None:
+        opts = getattr(opener, 'options', {}) or {}
+
             if 'revlogv2' in opts:
                 # version 2 revlogs always use generaldelta.
                 v = REVLOGV2 | FLAG_GENERALDELTA | FLAG_INLINE_DATA
             elif 'revlogv1' in opts:
+            v = REVLOGV1 | FLAG_INLINE_DATA
                 if 'generaldelta' in opts:
                     v |= FLAG_GENERALDELTA
             else:
-                v = 0
+            v = REVLOG_DEFAULT_VERSION
+
             if 'chunkcachesize' in opts:
                 self._chunkcachesize = opts['chunkcachesize']
             if 'maxchainlen' in opts: