mq: qpop: remove added files before re-adding removed files
We need to do this to avoid file/directories conflicts.
This causes patches removing a committed file and replacing it
with a directory to be "unpoppable".
% issue1810: inotify and fetch
adding foo
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding bar
adding spam
% issue1719: inotify and mq
% inserve
popping test.patch
patch queue now empty
% st should not output anything
applying test.patch
now at: test.patch
% st should not output anything