@ symbols also breaking when found in the last section of the path of the URL

Previously, a URL such as:
 > http://twitter.com/path/more@twitter

 is extracted to read:
 > http://twitter.com/path/more
 
but a similar path:
> http://twitter.com/path/more@twitter/

is not dropped in the same approach.

This fix adds the @ symbol as part of a general url path character, as it is allowed in code.
Here is a real world URL that brought this bug to light.
> http://www.stjohns.edu/alumni/pr_alu_130107b.news_item@digest.stjohns.edu%2falumni%2fpr_alu_130107b.xml?context_date=1/9/2013

A test was also added to check for this.