[Log] Provide a default log category for Y.log calls

Set a default log category of info if no category was specified, or the
category specified is not in the list of valid categories.
Merge remote-tracking branch 'andrewnicols/ylog-missing-categories' into dev-master
[core] Update HISTORY.md
YUI and Loader build for latest Gallery build
Merge branch 'dev-master' into dev-3.x

Conflicts:
	build/yui-base/yui-base-min.js
	build/yui-nodejs/yui-nodejs-min.js
	build/yui/yui-min.js
	src/yui/HISTORY.md