multiselect 5.x-2.0

changes from 5.x-1 to 5.x-2-BETA
http://drupal.org/node/284533
#196308: Missing description field
#227092: Scaleable?
#173500: Unresponsive script problem

changes from 5.x-2.0-BETA to the official 5.x-2.0 release
ensured select boxes don't flow around help text, included from #173500

- marked nodereference as an explicit dependency (since it always has been)
#179301: Fix JS compressor support

added checks to avoid errors that occur in admin/content, when the widget is used, but not populated.

included alt tags on image "buttons" for better usability.