merge: add _checkunknowndirs function for detecting path conflicts Add a new function which, given a file name, finds the shortest path for which there is a conflicting file or directory in the working directory. Differential Revision: https://phab.mercurial-scm.org/D779

merge: backup conflicting directories when getting files During batchget, if a target file conflicts with a directory, or if the directory a target file is in conflicts with a file, backup and remove the conflicting file or directory before performing the get. Differential Revision: https://phab.mercurial-scm.org/D778

merge: add merge action 'pr' to rename files during update Add a new merge action to handle a path conflict by renaming the conflicting file to a safe name. The rename is just to avoid problems on the filesystem. The conflict is still considered unresolved until the user marks the original path as resolved. Differential Revision: https://phab.mercurial-scm.org/D777

merge: add merge action 'p' to record path conflicts during update Add a new merge action to record path conflicts. A status message is printed, and the path conflict is added to the merge state. Differential Revision: https://phab.mercurial-scm.org/D776

commands: update the resolve command to handle path conflicts The resolve command must support displaying path conflicts and marking them as resolved or unresolved. Differential Revision: https://phab.mercurial-scm.org/D775

merge: add pathconflict merge state Path conflicts that occur during merges are represented by 'pu' (unresolved) and 'pr' (resolved) records in the merge state. These are stored on disk in 'P' records. Differential Revision: https://phab.mercurial-scm.org/D774