When read_only option was enabled, a user without SUPER privilege could
perform CREATE DATABASE and DROP DATABASE operations.

This patch adds a check to make sure this isn't possible. It also attempts to 
simplify the logic used to determine if relevant tables are updated,
making it more human readable.


mysql-test/r/read_only.result:
  Updated result file
mysql-test/t/read_only.test:
  A test case is added which shows that it is not possible to drop or create a
  database in read-only mode despite having the GRANT permissions to do so,
  SUPER user excepted.
sql/sql_parse.cc:
  - Simplified complex predicate by grouping it in a read friendly way.
  - Added predicate to fail on database updates while running in read-only
    mode.