Fixed a bug with "box-sizing" set to "border-box"

The date picker was broken if the page was having the "box-sizing" CSS
property set to "border-box", which is the default for most of the CSS
frameworks; Read more at
http://paulirish.com/2012/box-sizing-border-box-ftw/
Updated version number to 1.7.4
Updated reference to the minified file size
Another fix for the buggy positioning of the icon

While testing the date picker with various layouts and using different
CSS frameworks and resets, I discovered that the icon was wrongly
positioned most of the times.