INT 21 P - Phar Lap 386/DOS-Extender - EXECUTE PROGRAM                          
	AX = 25C3h
	ES:EBX -> pointer to parameter block (see #01377)
	DS:EDX -> pointer to 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. program filename
Return: CF clear if successful
	    all registers unchanged
	CF set on error
	    EAX = error code (see #01376)


(Table 01376)
Values for Phar Lap error code:
 01h	function code in AL is invalid ???
 02h	file not found or path invalid
 05h	access denied
 08h	insufficient memory to load program
 0Ah	environment invalid
 0Bh	invalid file format


Format of parameter block:
Offset	Size	Description	(Table 01377)
 00h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	32-bit offset of environment string
 04h	WORD	segment selector of environment string
 06h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	32-bit offset of command-tail string
 0Ah	WORD	segment selector of command-tail string