We use negative numbers for the compiler, and leave the possitive
numbers to match the Microsoft numbers:

-1	An Primary Expression was parsed, when a Type was expected.
	This happens because my parser knowledge is limited, and I
	am not good at writing grammars.  It is still an error,
	but if I were smarter, I would have found a Bison/Yacc way
	of handling it.

-2	Internal error, an interface is being defined inside an
	interface (This should never happen).

-3      Constant type is not one of sbyte, byte, short, ushort, int,
	uint, long, ulong, char, float, double, decimal, bool, string, enum
	or null type. 

-4	Operator should be unary

-5 	Operator should be binary