Fixing focus issue:

When disable_search flag is on, focus + hitting spacebar on the dropdown
causes the page to scroll and open the popup.
Adding preventDefault when the spacebar disables the scroll event to
happen.
Merge pull request #2046 from itayadler/master

Fixing focus issue:
Make all of Chosen use border-box
Merge pull request #2054 from harvesthq/chosen-box-sizing

Make all of Chosen use border-box
Merge branch 'master' into edge-detection