There was a wrong determination of the DB name (witch is
not always the one in TABLE_LIST because derived tables
may be calculated using temp tables that have their db name
set to "").
The fix determines the database name according to the type
of table reference, and calls the function check_access()
with the correct db name so the correct set of grants is found.
When reading a view definition from a .frm file it was
throwing a SQL error if the DEFINER user is not defined.
Changed it to a warning to match the (documented) case
when a view with undefined DEFINER user is created.
The check for view security was lacking several points :
1. Check with the right set of permissions : for each table ref that
participates in a view there were the right credentials to use in it's
security_ctx member, but these weren't used for checking the credentials.
This makes hard enforcing the SQL SECURITY DEFINER|INVOKER property
consistently.
2. Because of the above the security checking for views was just ruled out
in explicit ways in several places.
3. The security was checked only for the columns of the tables that are
brought into the query from a view. So if there is no column reference
outside of the view definition it was not detecting the lack of access to
the tables in the view in SQL SECURITY INVOKER mode.
The fix below tries to fix the above 3 points.
Changed the parser test for wildcards in hostname to checking for empty
strings instead (analogous with the test in default_view_definer()),
since wildcards do appear in the definer's host-part sometimes.
Item_type_holder doesn't store information about length and exact type of
original item which results in redefining length to max_length and geometry
type to longtext.
Changed the way derived tables except unions are built. Now they are created
from original field list instead of list of Item_type_holder.
