grep: extend functionality, add man page entry, add unit test. walkchangerevs now returns a two-tuple. Its behaviour is also extensively commented. The annotate command's getname function has been factored out to a new function, trimname, so it can be shared between annotate and grep. The behaviour of grep has been beefed up, so that it now performs a number of useful functions.

requesting all changes
abort: error: Connection refused
255
ls: copy: No such file or directory
requesting all changes
abort: HTTP Error 404: File not found
255