The fix is: if user has privileges to view fields and user has any
(insert,select,delete,update) privileges on underlying view 
then 'show fields' and select from I_S.COLUMNS table are sucsessful.


mysql-test/r/information_schema_db.result:
  Bug#20543 select on information_schema strange warnings, view, different schemas/users
  test result
mysql-test/t/information_schema_db.test:
  Bug#20543 select on information_schema strange warnings, view, different schemas/users
  test case
sql/sql_acl.cc:
  Bug#20543 select on information_schema strange warnings, view, different schemas/users
  checked that user has privileges on underlying view and if it's true
  set allowed_show to true for top view.
sql/sql_show.cc:
  Bug#20543 select on information_schema strange warnings, view, different schemas/users
  removed unnecessary rights check.'tables->allowed_show' check is used instead
sql/sql_view.cc:
  Bug#20543 select on information_schema strange warnings, view, different schemas/users
  skip the check of SHOW_VIEW_ACL privilege on underlying view. It is done later during
  execution of find_field_in_table_ref function.
sql/table.h:
  Bug#20543 select on information_schema strange warnings, view, different schemas/users
  'allowed_show' is set during rights check for view. If true then user has privileges 
  for 'show create view', etc