jquery < 1.5 is incompatible with CSP

[François Marier]

The version of jquery that's in squeeze (1.4.2) is incompatible with CSP:

  http://bugs.jquery.com/ticket/7371

and causes a warning like this one to show up in the Firebug console:

  CSP: Directive "inline script base restriction" violated
  window.script1343108620099=1;

Thankfully, squeeze-backports has jquery 1.6.4 and so we should bump the required version to 1.5 to force this.

(Found this solution on https://bugzilla.mozilla.org/show_bug.cgi?id=630882.)