revlog: use raw revision for rawsize
When writing the revlog-ng index, the third field is len(rawtext). See
revlog._addrevision:
textlen = len(rawtext)
....
e = (offset_type(offset, flags), l, textlen,
base, link, p1r, p2r, node)
self.index.insert(-1, e)
Therefore, revlog.index[rev][2] returned by revlog.rawsize should be
len(rawtext), where "rawtext" is revlog.revision(raw=True).
Unfortunately it's hard to add a test for this code path because "if l >= 0"
catches most cases.