Revise Controller_Rest to require an "entity" param for POST requests.
Rename two REST test classes in the gallery module.

--HG--
rename : modules/gallery/tests/Data_Rest_Test.php => modules/gallery/tests/Rest_Data_Test.php
rename : modules/gallery/tests/Items_Rest_Test.php => modules/gallery/tests/Rest_Items_Test.php
Fix class names for renamed tests, and move all other REST-related tests here.
None of these tests are edited yet - just a direct cut'n'paste.
Fix how Rest_Items::post_entity() deals with parent.
Revise how Controller_Rest::action_post() catches exceptions.
Fix how Rest_Items handles defaulting to the root item for GET.
We shouldn't check the method here... among other reasons, it screws up testing.
So, use Rest::get_response() instead.
Rewrite Rest_Data_Test and Rest_Items_Test for new REST API.
Merge pull request #426 from shadlaws/fixes_20130622

Fixes 20130622