Update jquery.bxslider.js

Improved cancellation functionality: 
- Cancellations in previous callbacks no longer force the cancel value; therefore you can cancel in onSlideBefore without it being effected by onSlideNext. And likewise you can choose not to cancel until onSlideNext.
- By default do not cancel navigation; default implementations of callback lambda functions return true; which means no cancellation.
Merge pull request #1 from snoop0x7b/master

Update jquery.bxslider.js