format_tags_string: fix typo
Changing error.php?mode=js from text/plain to text/javascript 

Changing the js mimetype to text/javascript to avoid problems with some proxy configurations.
support dc:date elements in rss and atom feeds
do not unlink lockfiles (closes #703)
Merge pull request #216 from PerryWerneck/master

Changing mimetype reported by errors.php?mode=js to avoi proxy problems.