Change metadata info so that that MIN() and code MAX() reports that they can return NULL. Bug #324


client/mysql.cc:
  Add column names for metadata when running with -T
mysql-test/r/show_check.result:
  test case for bug fix
mysql-test/t/show_check.test:
  test case for bug fix
sql/item_sum.cc:
  Change metadata info so that that MIN() and code MAX() reports that they can return NULL. Bug #324
sql/sql_load.cc:
  Removed not needed line