Add "notEqual" checks and validators

[kennedykori]

Add checks and validators for checking or ensuring that a numeric value is not equal to a given base value. The checkers should be preferably named notEqual and the validators should be preferably named requireNotEqual.

Example usage of notEqual

public int someMethod(int value) {
    if (notEqual(this.someBaseValue, value))
        return value;
    else
        return 0;
}

Example usage of requireNotEqual

public void setSomeValue(int value) {
    this.someValue = requireNotEqual(this.someBaseValue, value);
}