Allow default unit to be added to spinbox if not present

[interactivellama]

I'd call this a bug, since I think spinbox was meant to work this way, but it is a new initialization option.

Fixes #1490.

[swilliamset]

White space trouble. Input starts with a space between the number and the unit but them removes the space.

Also if I set the default unit to something besides the accepted units including null I get weird behavior.

    $('#mySpinbox2').spinbox({
        value: '10 px',
        min: 0,
        max: 10,
        step: 0.1,
        // decimalMark: ',',
        units: ['px'],
        defaultUnit: 'ouch'
    });

    $('#mySpinbox2').spinbox({
        value: '10 px',
        min: 0,
        max: 10,
        step: 0.1,
        // decimalMark: ',',
        units: ['px'],
        defaultUnit: null
    });

Granted these are fringe cases but should have better handling.

Feel free to use the config blocks above to write additional unit tests.

[interactivellama]

The defaults in our apps right now are no space whether tradition or intentional.

[interactivellama]

Updated with non-allowed default unit test.

I am not adding null. Non-strings should not be used, nor accounted for.

For instance options.units better be an array, since it used .length without checking to see if it's an array.

[cmcculloh-kr]

Breaks for any 3+ digit units

$('#mySpinbox2').spinbox({
    value: '1,0pxs',
    min: 0,
    max: 10,
    step: 0.1,
    decimalMark: ',',
    units: ['pxs'],
    defaultUnit: 'pxs'
});

[interactivellama]

Updated. Thanks.

[cmcculloh-kr]

You'll probably want to adjust this to account for units longer than 2

[interactivellama]

Refresh the page.

[cmcculloh-kr]

Please add a unit test for some unit/default unit combo that is 3+ digits and increments the spinbox at least once.

[interactivellama]

@cmcculloh Added test that uses rem and increments. Great suggestions!