This adds the pieces needs for memory testers to work in the makefile system
CONFIG:
MEMTEST86PLUS - which versions to snag of memtest86+
MEMTEST86 - which versions to snag of memtest
these are actually more just defined or undefined right now, as they snag the latest (who needs more than one version of a specific memory tester?)
memory_testers/Makefile:
Full makefile overhaul, includes switches for the two, now, supported memorytesters.