revlog: only allow lazy parsing with revlogng files
This will allow us to store indices in memory in a single entry format
#!/bin/sh
echo "[extensions]" >> $HGRCPATH
echo "mq=" >> $HGRCPATH
hg init a
cd a
echo 'base' > base
hg ci -Ambase -d '1 0'
hg qnew -mmqbase mqbase
hg qsave
hg qrestore 2