make revlog.addgroup pass its file handles to addrevision
This should fix issue255.
It looks like the problem there happens when addgroup calls addrevision
to add a full revision, and addrevision decides to split the index file
into a .i/.d pair. Since addgroup has an open file handle for the
index file, the renaming of the new .i file to its final name fails on
windows.
abort: Failed to parse .../t/.hg/hgrc
File contains no section headers.
file: .../t/.hg/hgrc, line: 1
'invalid\n'