VBOX: Attempt to gracefully fallback to using vboxmanage when the COM interface cannot be successfully created.

VBOX: Check for the cache disk configuration flag before attempting to query for the vm_image virtual disk.  There will be no vm_image virtual disk to unregister when cache disks are used with isocontextualization.

Mac installer: make my changes for OS 10.11 El Capitan compatibility work with branded versions of BOINC (GridRepublic, etc.)

... but change kill_program() so it's not a failure if the process doesn't exit.
This is to help debug a possible "zombie process" bug

The python version was failing cryptically.
For scripts that access the DB, I'd like to move from Python to PHP,
so that we have one less DB layer to maintain.

The scratch directory is created under the project folder.