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.

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644   a
755 * b/a
644 @ l
b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644   a
b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 755 * b/a
047b75c6d7a3ef6a2243bd0e99f94f6ea6683597 644 @ l
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l
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% should fail
abort: unknown revision '2'!
abort: please specify just one revision
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