Casting a 32-bit pointer to a uint64_t sign-extends!

Fixed by casting via uintptr_t
Handle print and print_when in bounds.

via handling return_second and if_then_else intrinsics

Fixes #308
Allow constant doubles to be treated as FloatImm (but emit a nasty warning)

This is mostly to give a better error message when people use double literals.

Fixes #285
Update copyright notice in LICENSE.txt

Clarify that copyright is not entirely owned by MIT CSAIL, but is instead still assigned to the contributors or their institutions (including MIT CSAIL).