[core] Fix coverage tests

The original coverage tests used yui-core-coverage and loaded the rest
of yui-base by inserting script tags. This seems to have been set up
that way to get more granular coverage information than just one entry
for yui-base, but it is causing YUI.add to fail in certain cases because
Loader is not yet available. This changes the coverage test to do the
same as the regular unit tests.
[core] Add missing `yui` module to coverage tests
Document app.showContent as chainable
Merge remote-tracking branch 'solmsted/patch-1' into live-docs
[app] Build

min files are no change.
Update package versions.
Replacement of @VERSION@ with new version.
[promise] Fix HISTORY.md to correctly reflect changes in 3.15.0
[App, Loader]: Update of history.
Whoopsie daisy. Add Graphics and Charts HISTORY.
[IO]: Update of history.
Add HISTORY entry for changes in `tap` event
Add HISTORY entry for reset('length') fix
Merge branch 'es-mod-coverage' into release-3.15.0
DataSchema: Ignore a test in Android < 3.
[YUI, Loader]: Build.
Update json files with new version number.
Merge branch 'release-3.15.0' into live-docs

Conflicts:
	build/model-sync-local/model-sync-local-coverage.js
Merge branch 'live-docs' into dev-master

Conflicts:
	build/yui-nodejs/yui-nodejs-min.js
	build/yui/yui-min.js
Merge branch 'dev-master' into dev-3.x