Fix loading jQuery in the offline reference

Currently, jQuery is being loaded from Google's CDN via a schemaless URI
reference "//ajax.googleapis.com/...". When the reference is viewed
offline, that URI reference resolves to "file://ajax.googleapis.com/...",
which causes two problems:

1) jQuery is obviously not loaded (can be checked by seeing whether the navbar
   remains pinned to the top of the page when scrolling). This is mitigated
   by the fallbacks on some pages that attempt to load the local copy of
   jQuery if the Google copy didn't load, although some pages lack the
   fallbacks.

2) More importantly, when viewed on Windows, this causes long browser freezes,
   as Windows tries to look up the script in a shared folder on
   ajax.googleapis.com, which only fails after a long timeout.

This commit fixes both problems by making the offline reference only
refer to the local copy of jQuery.
Merge pull request #365 from SpecLad/jquery-local

Fix loading jQuery in the offline reference