Fix a regression in HTML escaping for text area fields.
Fix a regression in HTML escaping for text area fields.

Text area fields were no longer escaping the HTML-unsafe characters
contained in the source text, either when dealing with plain text or
Markdown escaping.

We now escape the text in the base TextAreaField after normalizing it.

KnowNo/reviewboard,chipx86/reviewboard,brennie/reviewboard,1tush/reviewboard,1tush/reviewboard,sgallagher/reviewboard,bkochendorfer/reviewboard,sgallagher/reviewboard,1tush/reviewboard,sgallagher/reviewboard,1tush/reviewboard,KnowNo/reviewboard,KnowNo/reviewboard,chipx86/reviewboard,chipx86/reviewboard,davidt/reviewboard,brennie/reviewboard,sgallagher/reviewboard,bkochendorfer/reviewboard,bkochendorfer/reviewboard,brennie/reviewboard,bkochendorfer/reviewboard,custode/reviewboard,brennie/reviewboard,1tush/reviewboard,custode/reviewboard,davidt/reviewboard,beol/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,custode/reviewboard,custode/reviewboard,1tush/reviewboard,reviewboard/reviewboard,davidt/reviewboard,1tush/reviewboard,1tush/reviewboard,beol/reviewboard,KnowNo/reviewboard,reviewboard/reviewboard,davidt/reviewboard,1tush/reviewboard,beol/reviewboard,chipx86/reviewboard,beol/reviewboard