alias: improved diagnostic when arguments include --cwd, etc. The logic pre-emptively checks for -R, --repo, --repository and --cwd in order to give the user a more helpful error message. In addition, each option is handled invididually, which avoids listing them all in the error. Before: % hg --config alias.broken='push --cwd /dev/null' broken abort: Option --cwd may not be abbreviated! After: % hg --config alias.broken='push --cwd /dev/null' broken error in definition for alias 'broken': --cwd may only be given on the command line

perf: add perfrevlog function to check performance of revlog

revlog: add a flags method that returns revision flags

tag: do not allow tag names to consist solely of whitespace (issue2307) (simplification and test by mpm)