Strict mode now gives error if one tries to update a virtual column.

mysql-test/suite/vcol/r/vcol_column_def_options_innodb.result:
  Updated test results
mysql-test/suite/vcol/r/vcol_column_def_options_myisam.result:
  Updated test results
mysql-test/suite/vcol/r/vcol_keys_innodb.result:
  Updated test results
mysql-test/suite/vcol/r/vcol_keys_myisam.result:
  Updated test results
mysql-test/suite/vcol/r/vcol_misc.result:
  Added new test for 'show columns' and error handling when trying to update a virtual column.
mysql-test/suite/vcol/t/vcol_misc.test:
  Added new test for 'show columns' and error handling when trying to update a virtual column.
sql/sql_base.cc:
  Strict mode now gives error if one tries to update a virtual column.
sql/sql_show.cc:
  Show PERSISTENT instead of VIRTUAL for persistent columns.