Revert change to get_post_format() introduced in [24226].

see #24291

git-svn-id: http://core.svn.wordpress.org/trunk@24242 1a063a9b-81f0-0310-95a4-ce76da25c4cd
A better logic check for whether we are looking at a post formats supporting view.

see #24291.

git-svn-id: http://core.svn.wordpress.org/trunk@24243 1a063a9b-81f0-0310-95a4-ce76da25c4cd