reintroduces util.unlink, for POSIX and Windows. windows: factor it out of rename posix: add alias 'unlink' for os.unlink Note that this new unlink function now has different semantics than the unlink() we had before changeset 6bf39d88c857 ("rename util.unlink to unlinkpath").

opener: check exception for ENOENT

windows.rename: check OSError for EEXIST For example, if src has been opened with Python's open(), os.rename will raise EACCES. Continuing in that case is pointless.

perf: restore lazyindex hack This hack (and the module it lives in) exist so that performance can be compared across different hg versions.

revlog: pass rev to _checkhash

revlog: incrementally build node cache with linear searches This avoids needing to prime the cache for operations like verify which visit most or all of the index.