Better error handling in corner cases.

The app was crashing badly upon bogus input.

ie, unreachable URL's, URL'sthat aren't specs at all.

Fixed a couple of rules that were crashing in such cases.

Catching root errors sooner; good handling and proper user feedback is still missing, but at least it isn't crashing.
throw an error if body of the targetted url is empty
clear error messages before each run
fix options var name
revert changes following validator.js update
Fixed case when URL is inaccessible (it was still crashing).
Merge pull request #46 from w3c/tripu/misc-fixes

Better error handling in corner cases