worker: restore old countcpus code (issue4869) This is a backout of d29859cfcfc2. The stdlib implementation of multiprocessing.cpu_count() attempts to invoke a process on BSD and Darwin platforms (at least on 2.7). Under certain conditions (such as cwd being removed) this could raise. Our old code was silently catching the exception. The old code was more robust, so restore it.

filemerge: call premerge directly from main merge function The merge code currently does (in pseudocode): for f in tomerge: premerge f merge f We'd like to change this to look more like: for f in tomerge: premerge f for f in tomerge: merge f This makes sure as many files are resolved as possible before prompting for the others. This restructuring is also necessary for custom merge drivers. This function separates out the premerge step from the merge step. In future patches we'll actually turn these into separate steps in the merge driver. The 'if r:' occurrences will be cleaned up in subsequent patches.

bundle2: allow lazily acquiring the lock In the external pushrebase extension, it is valuable to be able to do some work without taking the lock (like running expensive hooks). This enables significantly higher commit throughput. This patch adds an option to lazily acquire the lock. It means that all bundle2 part handlers that require writing to the repo must first call op.gettransction(), when in this mode.