0.9.10.31

0.9.10.31
    Fix Darwin instability problems. Darwin isn't reliably firing
    SIGTRAP handlers, so use UD2 to generate a SIGILL instead of INT3
    to generate a SIGTRAP and we check for this in the SIGILL handler
    and DTRT if we see this by calling the sigtrap_handler
    ... Define TRAP that uses UD2 (0x0b0f or 0F 0B) instead on Darwin
        and INT3 elsewhere in x86-assem.S
    ... Removed the bogus sigaltstack (was Darwin only, now gone) in
        bsd-os.c that I added in the course of trying to fix this
        problem
    ... #+darwin use UD2 instead of INT3 in compiler/x86 and add
        support for disassembling this as break