OS_Exit, Quit process (application)

IN:
     IX = application handle returned from a previous OS_Poll
     BHL = pointer to stacked process information:
          B = 0, exit current process
          B <> 0, start instantiation of HL process handle and force OS_Bye via RC_QUIT

OUT, if call failed:
     Fc = 1
          A = RC_???
Registers changed after return:
     ..BCDEHL/IXIY same
     AF....../.... different