Fixes/changes:
1. Fixed many bugs in the external commands

New features:
1. Execution of DOG.DOG if DOG is invoked with -P SWITCH.
2. DOG - Backdoor interrupt
INT D0
		AL = 01h
		
Return:
	 AX = Version
	 
Notes:
Version is built up like this:

A H  A L
---  ---
| |	 | |
| |	 | +-- code maturity allways one of a (=alpha), b (=beta) OR f (=final)
| |  +---- Patchlevel
| +------- Minor version
+--------- Major version

(this implies that the maximum version for DOG is 15.15.15f ;)