[loader] Add support for optional dependencies
[loader] Ignore coverage for unreachable branch
[loader] Add HISTORY entry for optional dependencies
[loader] Ignore optional dependencies without a test
[loader] Document ignoring optional dependencies without tests
[loader] Ignore undeclared optional dependencies
[loader] Fail when requiring modules with failing tests
[loader] Fix access to undefined loader instance
Merge remote-tracking branch 'upstream/dev-3.x' into optional-require
[loader] Test correct attach order of optional dependencies
[loader] Check if requires list passes tests and add optionals to it

This way _sort() has knowledge of optional requires to sort them as
dependencies
[loader] Simplify _attach test for optional dependencies
[loader] Remove error from failing dependency tests
[loader] Fix attachment order test
[loader] Document loader._canBeAttached
[dom] Move out of color-base module

Currently, the `dom-style` module depends on `color-base` module only for
falling back to calculate computed style on legacy Opera (<= 12), but the
latest Opera (15+) is almost the same Chrome (`Y.UA.webkit` returns truth
actually). Many core modules are depending the `dom-style` module, I expect
that many YUI modules and applications will benefit to faster from more
than a little by this change. I also hope that this resolves #1621.
Merge branch 'dev-master' into dev-3.x
Fix left/right margin issues with dual-panel calendars
Merge branch 'dev-master' into dev-3.x

Conflicts:
	build/loader-base/loader-base-coverage.js
	build/loader-base/loader-base-min.js
	build/loader/loader-min.js
	build/yui-nodejs/yui-nodejs-min.js
	build/yui/yui-min.js
Add @andrewnicols as a committer.