Don't clobber and existing map install

This is a kludge to work around the fact that MAP is installed
via tarball and so bcfg2 will keep clobbering the install by
reinstalling it every time it is run.

We now check for a currently installed version number and only
install from tarball if it doesn't match the value of VERSION.
Merge pull request #33 from uobdic/dont-clobber-map-install

Don't clobber an existing map install