Fix file-changed-to-dir and dir-to-file commits (issue660). Allow adding to dirstate files that clash with previously existing but marked for removal. Protect from reintroducing clashes by revert. This change doesn't address related issues with update. Current workaround is to do "clean" update by manually removing conflicting files/dirs from working directory.

#!/bin/sh

hg init a
cd a
echo a > a
hg add -n
hg st
hg add
hg st

echo b > b
hg add -n b
hg st
hg add b
hg st
echo % should fail
hg add b
hg st

hg ci -m 0
echo % should fail
hg add a

echo aa > a
hg ci -m 1
hg up 0
echo aaa > a
hg ci -m 2

hg merge
hg st
echo % should fail
hg add a
hg st
hg ci -m merge

echo % issue683
hg rm a
hg st
echo a > a
hg add a
hg st