2 <CALL SYSOP jsys arg1 arg2 ....>
4 arg1...argn become acs 1...n. Unless it is a list of the form
5 (RETURN x) where x is register number to return or ALL to BLT
6 them into a UVECTOR called AC-VECTOR.
8 SIN,SOUT,GTJFN are hacked specially.
10 All JSYSs have ERJMP hack that return #FALSE (error-code) on failure.