Update loader and yui to optionally use pathogen encoding

Replaces https://github.com/yui/yui3/pull/1858

Need to test cross browser.
I believe the thought there is that Y.config.customComboBase will be set by the developer and the `p/` added on by the loader allowing for different urls.
```
Y.config.customComboBase = "http://cdn.yahooapis.com/combo/";
Y.config.customComboBase = "https://cdn.yahooapis.com/combo/";
``` 

I suppose its just as easy to set the `customComboBase` with the `p` included.
`https://cdn.yahooapis.com/p/`

I can easily change that.