refs #6089 get select order by desc working with clustering keys

git-svn-id: file:///svn/mysql.com/mysql-5.5.30@54783 c7de825b-a66e-492c-adef-691d508d4ae1
refs #6089 get index merge working with clustering keys

git-svn-id: file:///svn/mysql.com/mysql-5.5.30@54784 c7de825b-a66e-492c-adef-691d508d4ae1
refs #6089 fix mysql bug 50843 for clustering keys

git-svn-id: file:///svn/mysql.com/mysql-5.5.30@54785 c7de825b-a66e-492c-adef-691d508d4ae1
refs #6089 fix find_shortest_key to work with clustering keys

git-svn-id: file:///svn/mysql.com/mysql-5.5.30@54786 c7de825b-a66e-492c-adef-691d508d4ae1
refs #6089 fix mysql bug 57430, pick covering key over non-covering if they retrieve the same number of records

git-svn-id: file:///svn/mysql.com/mysql-5.5.30@54787 c7de825b-a66e-492c-adef-691d508d4ae1
refs #6089 query optimizer changes for clustering keys and joins

git-svn-id: file:///svn/mysql.com/mysql-5.5.30@54788 c7de825b-a66e-492c-adef-691d508d4ae1
refs #6089 have find_shortest_key prefer primary key over clustering key

git-svn-id: file:///svn/mysql.com/mysql-5.5.30@54789 c7de825b-a66e-492c-adef-691d508d4ae1