Introduce wp_safe_remote_request(). Also wp_safe_remote_head(), wp_safe_remote_get(), wp_safe_remote_post().

Reverts [24482].

Merges [24894] and [24895] to the 3.6 branch.

see #24646.



git-svn-id: https://core.svn.wordpress.org/branches/3.6@24896 1a063a9b-81f0-0310-95a4-ce76da25c4cd