Extract download_qunit_head.sh out.
Check QUnit.config.testDone existence to construct isMultipleLoggingCallbacksSupported variable.
Extract compare_with_expected_output.sh out to eliminate duplication.
Deprecate 'noPlan' option.

Now QUnit-TAP works as with 'noPlan: true' by default. To delare plan explicitly, 'QUnit.config.requireExpects' option is intended to be used instead.
Update README.
Regression suites should run off-line too.
Fix code comment a bit.