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.
running: init test1
result: None
running: add foo
result: 0
running: commit -m commit1 -d 2000-01-01 foo
result: None
running: commit -m commit2 -d 2000-01-02 foo
result: None
running: log -r 0
changeset: 0:0e4634943879
user: test
date: Sat Jan 01 00:00:00 2000 +0000
summary: commit1
result: None
running: log -r tip
changeset: 1:45589e459b2e
tag: tip
user: test
date: Sun Jan 02 00:00:00 2000 +0000
summary: commit2
result: None