Use a try/catch block to check for localStorage - fixes #1291, fixes #1688.

Accessing `window.localStorage` can immediately throw an exception, which needs to be caught.
For more information, see http://www.w3.org/TR/webstorage/#dom-localstorage.

See also http://mathiasbynens.be/notes/localstorage-pattern#comment-9.

I've tested this on my corporate PC running IE11 which was failing to load Meteor apps before. I think it is hard to add a test for `window.localStorage` throwing, but it should be an otherwise fairly innocuous change.