Return silently when external command triggers error - make hook accept hg command as string or as function object. - intercept dispatch.ParseError as well. Kudos to Steve Borho (TortoiseHg) for testing and debugging.

(0.9.2compat) implement external call handle and hook

Implement handle and hook for external callers Allows external callers that do not use the command line to pass current hg command to keyword extension. This implementation might change in the future, if wrapping of patch.diff is possible to the effect of avoiding external handles.