UI inconsistency: Number of media files under Manage / Media Library

[Denis-de-Bernardy]

Write a few test posts, upload a few test media files using the wp 2.5 media uploader.

Browse Manage / Posts: See lots of posts listed.

Browse Manage / Media: See lots of media listed.

Then, browse Options / Reading, set the number of posts per page to 1.

Browse Manage / Posts: See lots of posts listed.

Browse Manage / Media: See only one media listed. (not expected)

Expected result: lots of media listed.

[markjaquith]

(In [7458]) Always show 15 media files per page in the media manager (do not use front-of-house ppp setting). props Denis-de-Bernardy. fixes #6334