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.
# should print nothing
# should fail
abort: path 'b/x' is inside repo 'b'
abort: path 'b/x' is inside repo 'b'
# should fail
abort: path 'b/x' is inside repo 'b'
# should arguably print nothing
# should fail
abort: path 'b/a' is inside repo 'b'