merge: add a new 'backup' argument to get actions We're going to use this in an upcoming patch to back untracked files up when they're replaced by tracked ones.

_checkunknownfiles: turn 'conflicts' into a set We'll check for membership in this set in an upcoming patch.

checkunknownfiles: make control flow clearer In particular, make it clear that we only check for and abort on conflicts if force is not true.

_checkunknownfiles: rename 'aborts' to 'conflicts' In upcoming patches we'll be able to do more useful things than aborting.

origpath: move from cmdutil to scmutil This is a lower-level function so it doesn't need to be in cmdutil, and putting it here avoids a bunch of potential import cycle issues.

revlog: remove unnecessary cache validation in _chunks Previously, we likely called _chunkraw() multiple times in order to ensure it didn't change out from under us. I'm pretty certain this code had its origins in the days where we attempted to have thread safety of localrepository and thus revlog instances. revlog instances are already not thread safe for writing. And, as of Mercurial 3.6, hgweb uses a separate localrepository instance per request, so there should only be a single thread reading a revlog at a time. We more or less decided that attempting to make classes like revlog thread safe is a lost cause. So, this patch removes thread safety from _chunks. As a result, we make one less call into _chunkraw() when the initial read isn't serviced by the cache. This translates to savings of 4 function calls overall and possibly prevents the creation of an additional buffer view into the cache. I doubt this translates into any real world performance wins because decompression will almost certainly dwarf time spent in _chunks(). But it does make the code simpler, so it is an improvement.

revlog: return offset from _chunkraw() A subsequent patch will refactor _chunks() and the calculation of the offset will no longer occur in that function. Prepare by returning the offset from _chunkraw().