[maiko] bug in soft stack overflow handling code

[nbriggs]

In llstk.c:extendstack(), if the stack overruns the guard stack address and tries to generate a soft "stackoverflow" interrupt, it does so by setting extended_frame = 1 and the Lisp atom \PENDINGINTERRUPT = T, but later in the stack checking code we find \PENDINGINTERRUPT |= extended_frame -- which would turn the pending interrupt T (atom 76) into the atom U (atom 77), or if \PENDINGINTERRUPT happened to have become NIL by the time this happens, it would turn that into NOBIND.

I believe the extendstack() code should be setting extended_frame = T rather than 1.