INT 21 - European MS-DOS 4.0 - "AEXEC" - EXECUTE PROGRAM IN BACKGROUND
	AH = 80h
	CX = mode
	    0000h place child in zombie mode on exit to preserve exit code
	    0001h discard child process and exit code on termination
	DS:DX -> ASCIZA NUL-terminated ASCII string.	The ASCIZ string "ABC" consists of the four bytes 41h, 42h, 43h, and 00h.  Unless otherwise specified, maximum lengths given in the interrupt list do not include the terminating NUL. full program name
	ES:BX -> parameter block (as for AX=4B00h)
Return: CF clear if successful
	    AX = Command Subgroup ID (CSID)
	CF set on error
	    AX = error code (see #01680 at AH=59h/BX=0000h)
Program: European MS-DOS 4.0 was written for Siemens in Germany and then used
	  by several other European OEMs; its release falls between mainstream
	  versions 3.2 and 3.3
Desc:	asynchronously execute a program, creating a new process for it
Notes:	this function is called by the DETACH command
	there is a system-wide limit of 32 processes
	the CSID is used to identify all processes that have been spawned by
	  a given process, whether directly or indirectly
	programs to be run in the background must use the new executable format
	  (see #01596 at AH=4Bh)
	background processes may only perform asynchronous (background) EXECs,
	  either this function or AX=4B04h
	background processes may execute INT 11, INT 12, INT 21, INT 2A, and
	  INT 2F at any time; they may execute INT 10 and INT 16 only while
	  they have opened a popup screen via INT 2F/AX=1401h; no other
	  interrupts may be executed from the background
	background processes may not use drive B: or overlay their code
	  segments
	see AX=8700h for an installation check
	the "NE" new executable format made its first appearance in European
	  MS-DOS 4.0
SeeAlso: AH=4Bh,AH=87h,INT 2F/AX=1400h"POPUP"