Introduce email templates for automatic background updates.

The four templates are:
 1. We successfully updated their site. If any of their themes or plugins are out of date, it also mentions that. ('success')
 2. We are not configured to update their site, so we notify them of the new release. ('notify')
 3. We tried but failed to update their site. The error was early in the process, so no harm, no foul. This is the same as template #2, plus one sentence. ('fail')
 4. We tried to update their site, and failed while copying files. ('critical')

With assistance from markjaquith.

see #10787.


git-svn-id: http://develop.svn.wordpress.org/trunk@25837 602fd350-edb4-49c9-b593-d223f7449a82
Delete expired transients on database upgrades.

Reverts [25416], which had all transients being cleared. This leaves much to be desired, but we don't want a core update to be blamed for breaking a site that incorrectly assumes transients aren't transient.

props dartiss, pento.
fixes #20316.


git-svn-id: http://develop.svn.wordpress.org/trunk@25838 602fd350-edb4-49c9-b593-d223f7449a82
Awesome about page design for WordPress 3.7.

The page includes a giant password meter that serves as both an animated example and a working demo. How cool is that?

props jorbin, melchoyce.
see #25603.


git-svn-id: http://develop.svn.wordpress.org/trunk@25839 602fd350-edb4-49c9-b593-d223f7449a82
Remove rarr from about page text. Use a subtle background instead.

props markjaquith.
see #25603.


git-svn-id: http://develop.svn.wordpress.org/trunk@25840 602fd350-edb4-49c9-b593-d223f7449a82