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.

To run the tests, do:

cd tests/
python run-tests.py

See http://mercurial.selenic.com/wiki/WritingTests for
more information on writing tests.