1. Fixed the name of the table to proxies_priv
2. Fixed the column names to be of the form Capitalized_lowercase instead of
   Capitalized_Capitalized
3. Added Timestamp and Grantor columns
4. Added tests to plugin_auth to check the table structure
5. Updated the existing tests

Fix done by Georgi Kodinov,
now transferred to the 5.5.7 release build clone.