acl: use absolute_import Continuing the march towards Python 3.

checkunknown: audit path before checking if it's a file or link Previously we would lstat the file to see if it was a file or a link before attempting to process it. If the file happened to exist across a symlink, and if that symlink was pointing to a network file system, that check could be very expensive. The new logic audit's the path to avoid symlinks before performing the lstat on the file itself. In our situation, this shaved 10 minutes off of certain hg updates. 300 files * (2 seconds - the network filesystem lookup time)

pathauditor: change parts verification order to be root first Previously, when we verified the parts of a path in the auditor, we would validate the deepest directory first, then it's parent, and so on up to the root. If there happened to be a symlink in the chain, that meant our first check would likely traverse that symlink. In some cases that symlink might point to a network filesystem that is expensive, and therefore this simple check could be very slow. The fix is to check the path parts starting at the root and working our way down. This has a minor performance difference in that we used to be able to short circuit from the audit if we reached a directory that had already been checked. Now we can't, but the cost is N dictionary look ups, where N is the number of parts in the path, which should be fairly minor.