Show (short) list of possible enum values when an invalid value is encountered (resolves #1318)

All enum errors have (hopefully) been changed to a luax_enumerror, which has a
fixed error message. If additionally a list of valid options is passed, it
lists that in the error message. For every enum error with few options I've
implemented this using a getConstants call.

This solution has been designed specifically to reduce the number of template
instantiations (as I've been told that was a concern). All new template code
happens in places where there already was an instantiation of the relevant
StringMap. Of course there is still std::vector<std::string>...

--HG--
branch : minor

src/modules/math/wrap_Transform.cpp

@@ -140,7 +140,7 @@ int w_Transform_setMatrix(lua_State *L)
 		const char *layoutstr = lua_tostring(L, idx);
 		Transform::MatrixLayout layout;
 		if (!Transform::getConstant(layoutstr, layout))
-			return luaL_error(L, "Invalid matrix layout: %s", layoutstr);
+			return luax_enumerror(L, "matrix layout", Transform::getConstants(layout), layoutstr);
 
 		columnmajor = (layout == Transform::MATRIX_COLUMN_MAJOR);
 		idx++;