Import pintos project
Fix pintos makefiles to build on OSX

Use brew tap t3rm1n4l/homebrew-gcc_cross_compilers
* Install i386-elf-* toolchain
Fix pintos driver program environment paths

Also set QEMU as default emulator to be used.
Fix broken pintos shutdown with QEMU

QEMU recently removed support for bochs debug ports
Hence when running pintos, qemu gets stuck at Powering off
message.

Added support for using ACPI shutdown.