Context for theme install strings. Untranslate an error message until it can be cleaned up.

see #27453, #27055.


git-svn-id: https://develop.svn.wordpress.org/trunk@27610 602fd350-edb4-49c9-b593-d223f7449a82
Improve the autosave error message on nonce failure.

see #27453, #25272.


git-svn-id: https://develop.svn.wordpress.org/trunk@27611 602fd350-edb4-49c9-b593-d223f7449a82
Remove two new strings from post_preview().

see #25272, #27453.


git-svn-id: https://develop.svn.wordpress.org/trunk@27612 602fd350-edb4-49c9-b593-d223f7449a82