sqliterevmap: break ".hashes()" cycle in a safer way The `fromsvn()` revset implementation could cause weakref error when using sqliterevmap like: File "hgsubversion/util.py", line 357, in <lambda> return subset.filter(lambda r: tonode(r) in hashes) File "hgsubversion/maps.py", line 542, in __contains__ return self.get(key) != None File "hgsubversion/maps.py", line 533, in get for row in self.revmap._query( ReferenceError: weakly-referenced object no longer exists Basically the seemingly harmless assignment could break surprisingly: # dangerous: `hashes` does not have a reference of `meta.revmap` and may # become unavailable after `meta`, `revmap` being released by refcount. hashes = meta.revmap.hashes() The above syntax is nice to support while avoiding cycles is also nice. This patch removes `revmap._hashes` so the revmap no longer owns a reference of a `ReverseRevMap` object so the `ReverseRevMap` object no longer needs to use weakref for `self.revmap`. This could actually be caught by `comprehensive/test_sqlite_revmap.py`. I was not careful enough verifying the "fromsvn()" patch.

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