I've added three new functions to the ikiwiki VCS interface to support
renaming and removing files using the web interface. The mercurial and 
tla [[rcs]] backends need implementions of these functions.

(The maintainers of these backends have been mailed. --[[Joey]])

Also, currently git is the only VCS to have support for
[[untrusted_push|tips/untrusted_git_push]]. It _may_ be possible to
implement it for other DVCS, if they offer a hook that can be used to check
incoming pushes early.
