Performance improvement

To use the pattern /\(^\s\\+\)\@<=\%'.i.'c / instead of /\(^\s\\+\)\@<=\%'.i.'v / can improve the performance of the plugin.

I tried to open [jquery.js](http://code.jquery.com/jquery-1.9.1.js) and vim lagged for less than 1 second which reduces from about 2 seconds.