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/physics/Body.cpp

@@ -36,11 +36,16 @@ bool Body::getConstant(const char *in, Type &out)
 	return types.find(in, out);
 }
 
-bool Body::getConstant(Type in, const char  *&out)
+bool Body::getConstant(Type in, const char *&out)
 {
 	return types.find(in, out);
 }
 
+std::vector<std::string> Body::getConstants(Type)
+{
+	return types.getNames();
+}
+
 StringMap<Body::Type, Body::BODY_MAX_ENUM>::Entry Body::typeEntries[] =
 {
 	{"static", Body::BODY_STATIC},