Better Logic for deletion of build directory (for force clean build)

There have been several reported cases of people losing data due to Bamboo's deleting build directory for the force clean build option.

Having another think about it, I really think we need to separate out the logic for deletion of the build directory to be the responsibility of each of the individual repositories.

In particular the Perforce repository should be deleting the folder defined in the workspace mapping not the entire root (which is required for svn and cvs). I imagine it would be common to have the root set to a directory which has other stuff in it.