Grouped backports to the 4.5 branch.
- Posts, Post types: Apply KSES to post-by-email content,
- General: Validate host on "Are you sure?" screen,
- Posts, Post types: Remove emails from post-by-email logs,
- Pings/trackbacks: Apply KSES to all trackbacks,
- Comments: Apply kses when editing comments,
- Customize: Escape blogname option in underscores templates,
- Mail: Reset PHPMailer properties between use,
- Query: Validate relation in `WP_Date_Query`,
- Widgets: Escape RSS error messages for display.
Merges [54521], [54522], [54523], [54525], [54526], [54527], [54529], [54530], [54541] to the 4.5 branch.
Props voldemortensen, johnbillion, paulkevan, peterwilsoncc, xknown, dd32, audrasjb, martinkrcho, davidbaumwald, tykoted, johnjamesjacoby, ehtis, matveb, talldanwp.
Built from https://develop.svn.wordpress.org/branches/4.5@54560
git-svn-id: http://core.svn.wordpress.org/branches/4.5@54115 1a063a9b-81f0-0310-95a4-ce76da25c4cd
