update jquery.countdown to 1.6.3

Changes: https://github.com/kbwood/countdown/compare/Release_1_6_1...Release_1_6_3 (see file jquery.countdown.js)

Author changelog (http://keith-wood.name/countdown.html):
1.6.2:
* Don't recalculate target time if not supplied on option change
* Corrected clearing of labels when changing
* Corrected retrieval of time periods when paused
* Added Malayalam localisation
* Corrected Farsi and Korean localisations

1.6.3:
* Corrected layouts derived from markup
* Corrected timing callbacks for older IE