Switch cat command to use walk code. The old syntax of "hg cat FILE REV" is now obsolete. Use "hg cat -r REV FILE" instead, as for all other commands.

Add rename/mv command. This is the logical equivalent of copy and remove, and is in fact implemented as such. It doesn't use the remove command directly.

The copy tests don't need to invoke cp any longer.

Fix lots of exception-related problems. These have been around since the Big Code Split.

Merge with MPM.

Fix up copy command to behave more like regular "cp". In addition to recording changes, copy now updates the working directory.