Do not instantiate Chosen when IE7 or below
Use Microsoft's code snippet for browser detection

(http://msdn.microsoft.com/en-us/library/jj676915(v=vs.85).aspx#code-snippet-3)
Add IE_DOCUMENT_MODE into the Chosen object

Avoids adding another global variable
Move browser check into AbstractChosen as a class method. Make check more
efficient.
Rename browser check method
Merge branch 'master' into disable-chosen-prototype-ie7

Conflicts:
	chosen/chosen.jquery.js
	chosen/chosen.jquery.min.js
	chosen/chosen.proto.js
	chosen/chosen.proto.min.js
	coffee/lib/abstract-chosen.coffee