[jshint] Bugfix: Load sources to check in sync.

This is a quick-fix to avoid the following situation:

1. $("script").map makes an ajax request to load each source file and stores it in Screw.jshint_scripts.
2. A screw unit test is defined, where each Screw.jshint_scripts is checked against JSHINT.

Since the ajax calls where previously async, JSHINT sometimes already run, when ajax call was not yet finished.

This avoids the problem. In my local tests I could not see a slowdown larger than 1 second.
Merge pull request #9 from apepper/sync_jshint

[jshint] Bugfix: Load sources to check in sync.