Backup user needs PROCESS privilege when doing file-per-database backups

The following error occured:
mysqldump: Couldn't execute 'SELECT /*!40001 SQL_NO_CACHE */ * FROM `INNODB_BUFFER_PAGE`': Access denied; you need (at least one of) the PROCESS privilege(s) for this operation (1227)
Merge pull request #500 from nerdlich/patch-1

User needs PROCESS privilege when doing file-per-database backup