Skip protocol checking in esc_url() when we are dealing with a relative URL. Prevents munging of colons in paths and query strings, when present in a protocol-relative URL.

props SergeyBiryukov.
fixes #21974.



git-svn-id: https://core.svn.wordpress.org/trunk@24642 1a063a9b-81f0-0310-95a4-ce76da25c4cd