String cleanups

[nacin]

I'm auditing all new strings in 3.9. At the moment, translate.wordpress.org is claiming there is about 650 of them, but I think there is an accounting snafu somewhere. Regardless, this is usually a good opportunity to double-check formatting and context (not to mention style, content, and tone).

Already started with [27604] and [27605].

[nacin]

In 27609:

Add context to a string new to the admin.

Previously this string was used in TinyMCE on the frontend.

see #27453.

[nacin]

In 27610:

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

see #27453, #27055.

[nacin]

In 27611:

Improve the autosave error message on nonce failure.

see #27453, #25272.

[nacin]

In 27612:

Remove two new strings from post_preview().

see #25272, #27453.

[nacin]

In 27613:

Skipping placeholders in a string will only catch translators off guard.

see #27453, #27132.

[nacin]

In 27614:

Use an ellipsis instead of ...

see #27453, #27055.

[nacin]

In 27618:

TinyMCE strings: Merge, remove, reorganize, restore, clarify.

see #27453, #24067.

[nacin]

In 27620:

More translation cleanups.

Affects widgets (see #27112), custom headers (see #21785), theme installer (see #27055, reverts [27614]), and some media stuff. Untranslates some complicated strings that need additional study.

see #27453.

[nacin]

In 27645:

Merge two strings. see #27320, #27453.

[nacin]

In 27646:

Add context to 'Browse' (themes). see #27055, #27453.

[nacin]

In 27889:

Revert [27609] from the 3.8 branch, as it should have been applied to trunk. see #27453.

[azaozz]

In 27927:

TinyMCE: update translatable strings, see #27453, #24067

[nacin]

In 28140:

Add missing string translation in widgets.

see #27453, #27112.