Initial implementation of the hooked access callback...

...  Now have to make it get used everywhere.
Add hook_islandora_datastream_access()...

...  Also, start using our new access functions in a few places.
Add access checks to view/download links.
Add access checks.
Add a couple more access checks.
Add the strict access flag.
Use the hooked access callback in place of the any/all cases.

Leaving the functions called in place, in the case that they're called
elsewhere.
Pass the user along as we should.
Pass the content models...
The namespace check is handled via the hooked access callback.
Revert "Pass the content models..."

This reverts commit 2a654d6e837c4c8809d22b99bed731c1dc847e70...
The content models weren't needed or used... Messed up matching braces in
my head.

Conflicts:
	islandora.module
Return the final result from the permission anonymous functions.

...  Was missing... Also, the handling of an empty array of permissions
was happening only implicitly.
Add some basic tests for the hooked access callback.
Add missing function comment.
Squash ddebug_backtrace().
Change initial variable name.
Be somewhat more descriptive in API doc.
Get rid of non-strict policy enforcement.
Deprecate old and use new functions.
Themify datastream link creation.