largefiles: fix confusion upon removal of added largefile (issue3176) This patch makes "hg remove" work the same way on largefiles as it does on regular Mercurial files. If you try to remove an added largefile, the removal fails and you are instead prompted to use "hg forget" to undo the add.

  $ 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