0.9.1.29:

0.9.1.29:
        A number of signal handling cleanup/fixes:
        * fix gencgc/maybe_defer_handler race (thanks to Thiemo)
        * interrupt_maybe_gc (on cheneygc platforms): check for already
          pending handler before calling maybe_defer_handler in order
          not to lose interrupts
        * interrupt_handle_pending: check for the pending handler being
          null
        * run_deferred_handler: set the pending handler to null, before
          calling it to guard against the handler enabling interrupts ...
        * more defensiveness: enforce invariants: checks for signal masks,
          interrupts
        * refactoring: undoably_install_low_level_interrupt_handler wraps
          blockable handlers in low_level_maybe_now_maybe_later
        * don't unblock signals unconditionally in interrupt_maybe_gc_int just
          restore the sigmask from the interrupted context (kludge removed)
        * removed misguided sigprocmask calls from mips, hppa and sparc
          sig{trap,ill} handlers
        * removed non-x86 version of handle_breakpoint (interrupts are enabled
          in now common handle_breakpoint)
        * fixed arrange_return_to_lisp_function/post_signal_tramp to save and
          restore eflags (interrupt-threads seems to work)