Compares @value1 and @value2. If @value1 and @value2 cannot be
compared, the function returns GST_VALUE_UNORDERED. Otherwise,
if @value1 is greater than @value2, GST_VALUE_GREATER_THAN is returned.
If @value1 is less than @value2, GST_VALUE_LESS_THAN is returned.
If the values are equal, GST_VALUE_EQUAL is returned.
Compares @value1 and @value2. If @value1 and @value2 cannot be compared, the function returns GST_VALUE_UNORDERED. Otherwise, if @value1 is greater than @value2, GST_VALUE_GREATER_THAN is returned. If @value1 is less than @value2, GST_VALUE_LESS_THAN is returned. If the values are equal, GST_VALUE_EQUAL is returned.