Use chrome.runtime.lastError.message for rendering socket errors.

This is a built-in textual string. For additional information,
also still include the error code (turned into a positive number).
Use this in all calls in both ChromeSocket and RemoteDevice.

Resolves issue #193.
Fix sorting of internal window list.

The sort() method needs a <0/=0/>0 comparison result. The proper
method for doing this with strings is .localeCompare().
This fixes Alt-[PAGE]{UP,DOWN} ordering issues, where the selection
seems to jump around randomly.

While here, the usual syntax cleanup in window_list_test.js.
Merge pull request #202 from tvierling/textual_errors

Use chrome.runtime.lastError.message for rendering socket errors.
Merge pull request #200 from tvierling/window_list_sort

Fix sorting of internal window list.