merge: extract method for checking for conflicting untracked file Now that the functionality is collected in one place, let's extract it to a method.

merge: create 'cm' action for 'get or merge' case We still have one case of a call to _checkunknownfile() in manifestmerge(): when force=True and branchmerge=True and the remote side has a file that the local side doesn't. This combination of arguments is used by 'hg merge --force', but also by rebase and unshelve. In this scenario, we try to create the file from the contents from the remote, but if there is already a local untracked file in place, we merge it instead.

merge: don't overwrite untracked file at directory rename target When a directory was renamed and a new untracked file was added in the new directory and the remote directory added a file by the same name in the old directory, the local untracked file gets overwritten, as demonstrated by the broken test case in test-rename-dir-merge. Fix by checking for unknown files for 'dg' actions too. Since _checkunknownfile() currently expects the same filename in both contexts, we need to add a new parameter for the remote filename to it.