function isDigitSequence(sValue, oConstraints) {
		return oConstraints && oConstraints.isDigitSequence && sValue && sValue.match(rDigitsOnly);
	}
Checks whether isDigitSequence constraint is set to true and the given value is a digit
sequence.

@param {string} [sValue]
  the value to be checked
@param {object} [oConstraints]
  the currently used constraints
@returns {boolean}
  true if isDigitSequence is set to true and the given value is a digit sequence