nitdoc: makes quick-search field aware of paste from mouse.

Fixes #666

Démo sur stdlib: <http://gresil.org/jenkins/job/CI-nitdoc/ws/doc/stdlib/index.html>
Démo sur nitc: <http://gresil.org/jenkins/job/CI-nitdoc/ws/doc/nitc/index.html>

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>