Add check if typeaheadSource is function or not to fix onlyTagList true

typeaheadSource can be a function or object, if object needs to just check if typeaheadSource is $.inArray, else needs to call typeaheadSource and check if returned value is $.inArray
check if typeaheadSource is null before checking if is function or object
Merge pull request #129 from zkwentz/master

hotfix typeaheadSource check if object or function in pushTag (issue #125)