JavaScript maintenance

This fix a few trivial Javascript lint checks which should be harmless
although untested.

* jshintrc comes from Mediawiki core, I have slightly tweaked it to
  allow alert() and multiples "var" declarations.
* Fixed equalities to strict equalities.
* Some double quotes have been singled out.
* Missing semicolon (some of them might still be need to be added).

Change-Id: I846d5a87f8761aec1d3897a35a1d12c8f85b916f
Merge "JavaScript maintenance"