Build: Enable jscs linelength check, fix many too-long lines

Mostly adds linebreaks to long strings, sometimes renames variables or edits module and test names to make them shorter. Updates grunt-jscs to allow disabling for the code from external/jsdiff.js. Keeps excluding test/deepEqual.js from grunt file, still has 1000+ errors even without line length check.

Fixes #654
Ah, right. Our separate files aren't valid. They have to be concatenated to validate (normally one would run jscs/jshint on individual files, not on the concatenated result, but we're not there yet).