largefiles: remove overly complex handling of ignored and unknown files

largefiles: introduce basic debugstate --large functionality Very useful for debugging largefiles "performance" issues. This is used for testing 03faf12fbee7.

util: fold ENOENT check into unlinkpath, controlled by new ignoremissing flag Refactor a common pattern.

merge with stable

largefiles: don't walk through all ignored files Problem: 'hg status' with largefiles enabled would walk through all the files that .hgignore said should be ignored. That made it slow if a lot of files were .hgignored or the cache was cold. It seems like there was a reason to this, but other improvements has rendered this unnecessary. Solution: .hgignore is now only ignored when that is requested (--ignore). This is a minimal 'stable' change. There is room for other improvement.

largefiles revert: update lfdirstate with result from first cleanliness check Largefiles revert do for some reason have two lfdirstates and lfdirstatestatus invocations in one function. The result from the first lfdirstate check was however not written back to the lfdirstate, and some files was thus checked twice.

largefiles status: update lfdirstate with result from cleanliness check Problem: 'hg status' kept checking largefiles with an unknown state until some other command wrote the updated dirstate. Solution: Add missing lfdirstate.write().

bundlerepo: don't return the peer without bundlerepo from getremotechanges Problem: getremotechanges would return the 'other' repo if nothing was incoming and there thus wasn't any bundle to base the repo on. The 'other' could be a http peer which only implement the functionality available over the http protocol. Transplant could thus fail with TypeError: argument of type 'httppeer' is not iterable Solution: Return the local repo instead of the remote peer if there is no reason to place a bundlerepo on top of the local repo.

strip: do not update branchcache during strip (issue3745) At this moment, the cache is invalid, and will be thrown away. Later the strip function will call the `localrepo.destroyed` method that will update the branchmap cache.

copies: do not track backward copies, only renames (issue3739) The inverse of a rename is a rename, but the inverse of a copy is not a copy. Presenting it as such -- in particular, stuffing it into the same dict as real copies -- causes bugs because other code starts believing the inverse copies are real. The only test whose output changes is test-mv-cp-st-diff.t. When a backwards status -C command is run where a copy is involved, the inverse copy (which was hitherto presented as a real copy) is no longer displayed. Keeping track of inverse copies is useful in some situations -- composability of diffs, for example, since adding "a" followed by an inverse copy "b" to "a" is equivalent to a rename "b" to "a". However, representing them would require a more complex data structure than the same dict in which real copies are also stored.