tests/test-extra-filelog-entry.t

largefiles: simplify lfutil.writehash

This was unnecessarily verbose: there is no need to unlink the file
when we open it for write anyway, and there is no need to check if the
file exists after we created it.

Issue351: mq: qrefresh can create extra revlog entry

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "mq=" >> $HGRCPATH

  $ hg init
  $ hg qinit

  $ echo b > b
  $ hg ci -A -m foo
  adding b

  $ echo cc > b
  $ hg qnew -f foo.diff
  $ echo b > b
  $ hg qrefresh

  $ hg debugindex b
     rev    offset  length   base linkrev nodeid       p1           p2
       0         0       3      0       0 1e88685f5dde 000000000000 000000000000