Changes 0.5.2:
* TinyMCE 3.4.2 now compatible with IE9
* PEAR::Net_SMTP 1.5.2, fixed timeout issue
* Fix bug where template name without plugin prefix was used in render_page hook
* Support 'abort' and 'result' response in 'preferences_save' hook, add error
  handling
* Fix bug where some content would cause hang on html2text conversion
* Improve space-stuffing handling in format=flowed messages
* Fix bug where some dates would produce SQL error in MySQL
* Added workaround for some IMAP server with broken STATUS response
* Fix bug where default_charset was not used for text messages
* Stateless request tokens. No keep-alive necessary on login page
* Force names of unique constraints in PostgreSQL DDL
* Add code for prevention from IMAP connection hangs when server closes socket
  unexpectedly
* Remove redundant DELETE query (for old session deletion) on login
* Get around unreliable rand() and mt_rand() in session ID generation
* Fix some emails are not shown using Cyrus IMAP
* Fix handling of mime-encoded words with non-integral number of octets in
  a word
* Fix parsing links with non-printable characters inside
* Fixed de_CH/de_DE localization bugs
* Add variable for 'Today' label in date_today option
* Applied plugin changes since 0.5-stable release
* Fix SQL query in rcube_user::query() so it uses index on MySQL again
* Use only one from IMAP authentication methods to prevent login delays
* Fix strftime format support in date_today option
* Removed redundant </form> tags from contact add/edit pages
* Fix CSS error in contact details screen on IE7

(adam)