INT 2F - DOS 5+ TASK SWITCHER - FREE SWITCHER ID                                
	AX = 4B04h
	BX = switcher ID
	ES:DI -> task switcher entry point (see #02819)
Return: AX = 0000h
	BX = status
	    0000h successful
	    other error (invalid ID or ID not allocated)
Notes:	called by a task switcher when it exits, unless it was the first loaded
	  and is providing the support for AX=4B03h and AX=4B04h
	the task switcher providing the identifiers may call the terminating
	  task switcher's entry point as needed
	this call is available from within DOSSHELL even if the task switcher
	  is not installed
	this call is supported by PCIBM PC Tools v8+ CPTASK, but appears to return
	  sucessfully no matter which ID is given
SeeAlso: AX=4B02h,AX=4B03h