MSR1: 0.5.1

This maintenance release contains critical bug fixes for 0.5:

[Fixed] Casper not working in IE
[Fixed] Cannot delete users on MySQL
[Fixed] Lost work if logged out while editing
[Fixed] Possible to downgrade Owner user
[Fixed] If author changes post author they lose access to post
[Fixed] Weird status code when authorising
[Fixed] Errors when uppercase used in /ghost/ URL
[Fixed] UUID validation error when importing
[Fixed] No notification for errors when sending mail

Full changelog