Blender Git Loki

Tweak to the changes from r26820 (nuking scons install directory):

Those changes made developing Blender using scons as buildsystem impractical. They were nuking my various configs everytime I compiled resulting in a long wait for all the files to get copied over again at the end, or else I'd have to manually go scouting out files to copy over.

Now, made this only nuke the scripts directory there which IMO solves the main issues that the original commit intended to solve (outdated scripts lingering in that folder, and mixing with the new ones).

If there are complaints that only doing the scripts dir is not enough, then we better just make this destructive stuff an optional thing (i.e. by default, nuking will still occur, but at least developers can disable)