Fixing unrequired var in the streams driver.

$namespace is only required if $stream is a slug, so these should all have a default null value.
Adding SITE_REF sub folder.

In order to work on Pyro Pro, the files need to be in their own SITE_REF folder.

If you are upgrading from beta1 or beta2, you'll need to move any folders in page_types into page_types/default.

Closes #2264.
Fixing sync for SITE_REF page_types folders.

Should have been in previous commit.
Fixing issue with includes in streams.

This was previously an AND where when it should have been an OR where.