Prevent granting permission that differs from a defined action by case only

[Ryan J Ollos]

The following issue was reported in ​gmessage:trac-users:vKI_MDGL-Fs/ecyzUJLqBAAJ. The user had granted TRAC_Admin to a user, and when attempting to grant TRAC_ADMIN, the system replied that the user already had TRAC_ADMIN. I haven't tried to reproduce yet with MySQL.

It would seem that the most straightforward way to avoid confusion would be to prevent users from adding a permissions group that differs from a defined action only by case. Further, to handle the scenario in which a component is enabled after a permission is granted we should provide a more accurate error message, showing the actual casing of the permission that has already been granted.