Abort and error handling massively overhauled:
Kevin Bracey authored
  Aborts now give standard error messages (Abort on Data Transfer at... etc)
  *ShowRegs now filled in after aborts
  assert(), abort(), "free failed" and standard signal handlers now use Wimp
    error boxes if in the desktop
  Postmortem button on error boxes to view the postmortem

Also, x$multiply, x$divide, __rt_sdiv, x$remainder, x$udivide, __rt_udiv and
x$uremainder optimised.

Version 5.35. Tagged as 'RISC_OSLib-5_35'
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