Emacs: document existing functions.

Emacs support: add hg-revert-buffer.

Fix callers to file.revision to use file.read This was causing unchanged files to show up as modified.

Clean up some merge logic - rename mode to branch_merge - use explicit update mode - use negative mtime for updates that set mtime - expand some cryptic variable names - elaborate merge dirstate comments - remove redundant manifest lookup for non-merge case - remove impossible merge case - fix up test cases

Fix up some bugs introduced by recent merge changes - use new changed list to track what files actually got new revlog entries at commit/rawcommit time - when updating a file during a merge, don't mark it as completely unchanged - handle file not being in parent 1 in status

merge: remove remaining mark bits

Fix long-standing excessive file merges Since switching to the multihead approach, we've been creating excessive file-level merges where files are marked as merged with their ancestors. This explicitly checks at commit time whether the two parent versions are linearly related, and if so, reduces the file check-in to a non-merge. Then the file is compared against the remaining parent, and, if equal, skips check-in of that file (as it's not changed). Since we're not checking in all files that were different between versions, we no longer need to mark so many files for merge. This removes most of the 'm' state marking as well. Finally, it is possible to do a tree-level merge with no file-level changes. This will happen if one user changes file A and another changes file B. Thus, if we have have two parents, we allow commit to proceed even if there are no file-level changes.