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JSYS error

It is now the case that JSYS calls which are followed by
a JUMP (of any kind, not just ERJMP and ERCAL) which cause
an illegal instruction trap, that the Lisp trap handler
will resume the computation at the effective address of
the JUMP instruction (normally JUMP is a  no-op).

By careful coding, it is possible to write JSYS calls
which will not cause a "TRAP AT LOCATION" either on

In addition, any JSYS trap in which the next instruction
after the JSYS is a JFCL is assumed to be a "user JSYS"
(i.e. rather than one of the ones in the system which
are "critical region") and, rather than a TRAP AT LOCATION nnnn
being executed, the error, JSYS ERROR (error number 0)
is invoked.

The "offender" (CADR (ERRORN)) of error 0 is always the
error code. This permits an ERRORTYPELST entry which
would print the error message out.