Fix for trim function call in tags.js that causes error in IE8

Internet Explorer 8 doesn't support the <string>.trim() function, see http://msdn.microsoft.com/en-us/library/ie/ff679971(v=vs.94).aspx.  We still have to support this version internally which is how we noticed the problem.

So have simply replaced the existing call with its jQuery equivalent.

Hope this is of use to you?  This is my first pull request btw, so please forgive me if I've done anything incorrectly :)

Cheers,
Mike.