Fixed wrong key length when using MIN() optimization (non fatal, but caused InnoDB to write warnings to the log file)
This fixed bug #11039: InnoDB: Warning: using a partial-field key prefix in search


mysql-test/r/innodb.result:
  Added extra test for bug #11039: InnoDB: Warning: using a partial-field key prefix in search
mysql-test/t/innodb.test:
  Added extra test for bug #11039: InnoDB: Warning: using a partial-field key prefix in search
sql/opt_sum.cc:
  Fixed wrong key length when using MIN() optimization