Few words on programming interface functions.
--------------------------------------------

For now exact way is to be defined. Few assumtions that can/must be made:

- Values passed to interface function should always be of type given in
	definition or one of its descendants. It is up to LangX compiler to assure
	all needed upcasts are done. Testing argument type, if really needed
	should be done trough getVMType(). Normally it is not a case.
- String pointers are never null - they can point to "", but can be
	resolved without problems. 
- VMObject pointer CAN BE NULL !!! You should ALWAYS check it in interface
	function and return nice value. ( There may be one exception from this 
	rule - maybe I will provide method-like interface with 'this' pointer
	guaranteed to be not null)