[PATCH 0 of 4] Merge working dir patching and dirstate updating

[Patrick Mezard]

Working directory files patching and dirstate updating are currently two
separate operations. In practice, all callers always perform both actions.
Merging them at patch.py API level will make patching easier for everyone while
allowing interesting refactorings like abstracting all file system access in
patch.py.

This change is likely to break many history rewriting extensions, see the diffs
applied to mq for more details.