Stop the button from resizing when content changes

[scottgrayson]

If you want to show a spinner, checkmark, x, or change the text:
the button should not get any smaller than the initial width

bad ( this happens currently )

[ submit ]
[ x ]

good ( not yet implemented )

[ submit ]
[ x ]

good ( should already work )

getting bigger to fit more text is also good
[ save ]
[ success ]