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
