Too many improvements and fixes since 1.5.1 to mention. Important feature additions include:
* Better search. Alternate implementations can be easily configured in app.yml. apostropheMysqlSearchPlugin is now standard in the sandbox and is a lot more convenient to configure and integrate than Lucene.
* Better caching and session management. The provided aMysqlCache class implements caching in the MySQL database rather than cluttering the filesystem and is much more flexible about the content of keys. The sandbox now uses this class together with sfCacheSession (note that you need a recent release of Symfony 1.4 since we contributed a bug fix to that class).
* Better concurrency in The aLock interface and the aLockFlock and aLockPkLockServer implementations of that interface.
* OPTIONAL support for jQuery 1.7.x (NOT enabled by default, you must explicitly switch to jQuery 1.7, we are NOT breaking bc with jQuery 1.4.3).
* Many classes refactored to allow easy overrides (BaseaHtml? and aHtml, for instance).
* Many fixes and improvements to minify and LESS support.
* Support for alternate rich text editors, notably apostropheCkEditorPlugin. The sandbox now uses CKEditor.
* Support for manipulating media and data files that are implemented by PHP stream wrappers such as aS3StreamWrapperPlugin for cloud based hosting.
* standardArea component provides a more convenient way to insert a typical content area with a typical set of slots. You can easily override the list of slots, both in app.yml and programmatically.
* More media embed services.
