Allow to skip cleaning working dir
Allow projects to skip the cleaning of the working dir for faster build. Things like yeti would greatly profit in build speed from keeping nml cache files for graphics.
This could be implemented in .devzone/build/
Whether the type file or some new files should be used - unsure. Needs thinking a bit. It could need a build parameter to clear the working dir regardless.
Conversely also the option to only keep nml's cache files could be used (and possibly makes also sense): hg purge --all --exclude *cache or similar would be of utility.