Attempt to launch headless browser.
1.5.4
Use html5 doctype

Without a valid doctype, IE will use “quirks mode” which is bad times.
For example, it will make IE9 behave like IE8 so methods like
`Array.prototype.indexOf` will suddenly be missing.
1.5.5
allow the user to specify the test harness via argv
1.5.6
Add nice message, .gitignore.
no gitignore
1.5.7
be less annoying
don't check headless on linux or bsd
1.5.8
Unbreak `testling -u` on OS X

This fixes two problems that were preventing `testling -u` from working.

1) Need parens with the ternary operator to make it do what you were
actually intending.

2) Check for -u argument first so that the “friendly message” doesn’t
terminate the process early. This bug was introduced here:
https://github.com/substack/testling/commit/9aa50c4bb45bc0fa78ea7aa5d828
d8491a2b891a