@Override
    public void putExtraOption(String key, Object value)
    {
        if (extraOptions.put(key, value) != null)
            throw err("Duplicate proto option: " + key, this);
    }
Returns the java package name that was configured in the proto. Note that {@link #getJavaPackageName()} will have
the same value as this, if the compiler options did not have entries that override it.
protostuff-parser/src/main/java/io/protostuff/parser/Proto.java