NzbDrone v1533 - Added SPK compatibility for built-in NzbDrone updates!

SPK now versioned by date for multi-branch and built-in NzbDrone updater compatibility - SPK upgrade now retains current NzbDrone binary (avoids potential binary downgrade) when necessary
added ``` SPK_VERS = $(shell date +%Y%m%d) ``` and changed cross to pull current/latest master