An UNIQUE KEY consisting of NOT NULL columns
  was displayed as PRIMARY KEY in "DESC t1".
  According to the code, that was intentional
  behaviour for some reasons unknown to me.
  This code was written before bitkeeper time,
  so I cannot check who and why made this.
  After discussing on dev-public, a decision
  was made to remove this code


mysql-test/r/key.result:
  Adding test case.
mysql-test/t/key.test:
  Adding test case.
sql/table.cc:
  Removing old wrong code