Fixed #10675 -- Added unicode paragraph and line-sep handling to escapejs.

There were a couple of line breaking Unicode characters (\u2028 and
\u2029) that cause Javascript errors, at least in Firefox, if not
escaped. So now we do so. Based on a patch from rleland.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10543 bcc190cf-cafb-0310-a4f2-bffc1f526a37