convert: fix convert dropping p2 contents during filemap merge When converting a merge commit using a filemap convert (i.e. when moving contents from the root of the repo into subdir1/), convert would silently drop the entire contents of the target repo's p2. This was because when it built the target commit, it did so by taking the target p1 and adding only the files that changed in the source repo's merge commit. This breaks in the case where the target repo has files that are unrelated to the source repo (like in the case where you use convert to import a repo as a subdirectory of another). The fix is to use Mercurial's merge logic to detect which files in p2 we should carry over to the merge. It follows three rules: 1) if the file belongs to the source, don't try to merge it. Rely on the list of files provided to putcommit to be correct. 2) if the file requires merging or user input (change vs deleted), throw an exception. We don't have enough info to do this. 3) if p2 has the newest, non-merge-requiring version of the file, take it I've also added a test to cover this issue.