cext: fix Windows warning about implicit conversion of 32-bit shift to 64 bit
mercurial/cext/revlog.c(1541) : warning C4334: '<<' : result of 32-bit shift
implicitly converted to 64 bits (was 64-bit shift int ended?)
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state