Prevent 100% CPU hang on certain input text.

John Gruber's "Improved Liberal, Accurate Regex Pattern for Matching URLs"
(https://gist.github.com/gruber/249502) has three unnecessary `+` operators,
which cause O(N^3) performance issues on certain inputs containing
parentheses.  This was causing a hang in the attributions of
[[:pt:Ficheiro:Joseph_Ducreux_(French_-_Self-Portrait,_Yawning_-_Google_Art_Project.jpg]]
in a large book containing Portuguese articles on the human sensory
system.

Change-Id: I56890b98efbee3c05cbce1a125606bb03af07eb3