Spec whitespace + mocha.ignoreLeaks(true)

Split off the spec/style related stuff from #2121.

 - Change the title for the spec runner to 'Leaflet Spec Runner'
 - spaces to tabs in the runner.
 - Ignore leaks for mocha (https://github.com/visionmedia/mocha/commit/d6330cb678511f371a47c95accbef93ecb092c9c)
 - whitespace, quote use and an unused var in `UtilSpec.js`

Makes me wonder why no style is enforced for the spec: https://gist.github.com/jieter/7212532 shows the list of errors for a version of [Leaflets jshintrc](https://github.com/Leaflet/Leaflet/blob/master/build/hintrc.js) with some relaxations applied...