Added 'or else' construct to script language.

git-svn-id: svn://svn.code.sf.net/p/magicseteditor/code/trunk@423 0fc631ac-6414-0410-93d0-97cfa31319b6

src/script/script.hpp

@@ -70,6 +70,8 @@ enum BinaryInstructionType
 ,	I_GT			///< operator >
 ,	I_LE			///< operator <=
 ,	I_GE			///< operator >=
+// Error handling
+,	I_OR_ELSE		///< if a != error then a else b
 };
 
 /// Types of ternary instructions (taking three arguments from the stack)