dirstate: rename forget to drop
It has substantially different semantics from forget at the command
layer, so change it to avoid confusion.
We can't simply combine it with remove because we need to explicitly
drop non-added files in some cases like commit.
$ hg init rep
$ cd rep
$ mkdir dir
$ touch foo dir/bar
$ hg -v addremove
adding dir/bar
adding foo
$ hg -v commit -m "add 1"
dir/bar
foo
committed changeset 0:6f7f953567a2
$ cd dir/
$ touch ../foo_2 bar_2 con.xml
$ hg -v addremove
adding dir/bar_2
adding dir/con.xml
adding foo_2
warning: filename contains 'con', which is reserved on Windows: 'dir/con.xml'
$ hg -v commit -m "add 2"
dir/bar_2
dir/con.xml
foo_2
committed changeset 1:6bb597da00f1
$ cd ..
$ hg init sim
$ cd sim
$ echo a > a
$ echo a >> a
$ echo a >> a
$ echo c > c
$ hg commit -Ama
adding a
adding c
$ mv a b
$ rm c
$ echo d > d
$ hg addremove -n -s 50 # issue 1696
removing a
adding b
removing c
adding d
recording removal of a as rename to b (100% similar)
$ hg addremove -s 50
removing a
adding b
removing c
adding d
recording removal of a as rename to b (100% similar)
$ hg commit -mb