make DynamicWorkspace more thorough.
make DynamicWorkspace more thorough.

Note: there's still a bug due to our failure to inform
the old layouts to clean up.

darcs-hash:20070814014548-72aca-9b66ee3deba31a15b6e0b0dd0b79847edc6fc6e3

jthornber/XMonadContrib,jthornber/XMonadContrib