INT 21,29 - Parse a Filename for FCB

	AH = 29h
	AL = bit pattern to control parsing (see bit meanings below)
	DS:SI = pointer to a filespec to parse
	ES:DI = pointer to a buffer for unopened FCB


	Bit patterns for parsing control found in AL:

	|7|6|5|4|3|2|1|0|  AL
	 | | | | | | | `---- 1 = ignore leading separators
	 | | | | | | |	     0 = don't ignore leading separators
	 | | | | | | `----- 1 = modify drive ID if specified
	 | | | | | |	    0 = modify drive ID regardless
	 | | | | | `------ 1 = modify filename if specified
	 | | | | |	   0 = modify filename regardless
	 | | | | `------- 1 = modify extension if specified
	 | | | |	  0 = modify extension regardless
	 `-------------- unused

	on return:
	AL = 00 if no wildcard characters present
	   = 01 if wildcards present in string
	   = FF if drive specifier is invalid
	DS:SI = pointer to the first character after parsed filename
	ES:DI = pointer to the updated unopened FCB


	- retrieves filename from the command line string and places
	  the filename components into an unopened FCB for later use
	- if no filename is found a pointer is returned in ES:DI that
	  has a blank at ES:DI+1
	- this function can be used to detect the existence of logical DOS
	  drives by creating a dummy filespec with a drive letter and colon
	  prepended.  If the drive is invalid, this function will return FF
	  in AL