fixes "similar" tags clash when @ is already in textarea
fixes "similar" tags clash when @ is already in textarea

For example, see: https://www.dropbox.com/s/l6y615q4636zr81/Screenshot%202015-06-29%2018.49.50.png?dl=0

To reproduce, go here: http://podio.github.io/jquery-mentions-input/ and try tagging:
-@ken and choose first result
-@ken and choose second result
-@au and choose one option

Result is https://www.dropbox.com/s/l6y615q4636zr81/Screenshot%202015-06-29%2018.49.50.png?dl=0 because the script doesnt find the "closest" @. We realized this as in our implementation we are keeping the "@" (so the mention ends up like: @someUser123), but it can be reproduced when you are using emails, or basically any word with "@"..
ABeloeil/jquery-mentions-input,podio/jquery-mentions-input,ABeloeil/jquery-mentions-input,podio/jquery-mentions-input