function copySymbols(source, meaning) {
                if (meaning) {
                    for (var id in source) {
                        var symbol = source[id];
                        copySymbol(symbol, meaning);
                    }
                }
            }
Copy the given symbol into symbol tables if the symbol has the given meaning
and it doesn't already existed in the symbol table
@param key a key for storing in symbol table; if undefined, use symbol.name
@param symbol the symbol to be added into symbol table
@param meaning meaning of symbol to filter by before adding to symbol table