Double attribute escaping for post attachments

[dwc]

When the rich editor is off, editing attachments causes the description field to be double encoded. This is due to the use of htmlspecialchars, when the value is already encoded in sanitize_post_field.

Switching to attribute_escape fixes this; I'll attach patches for 2.7 and trunk.

[sambauers]

This should use wp_specialchars, not attribute_escape. The new wp_specialchars does not double encode entities by default.

[dwc]

Use wp_specialchars instead of attribute_escape

[dwc]

Use wp_specialchars instead of attribute_escape

[ryan]

(In [10700]) Avoid double encoding of attachment descriptions. Props dwc. fixes #9168 for trunk

[ryan]

(In [10701]) Avoid double encoding of attachment descriptions. Props dwc. fixes #9168 for 2.7