refs #6090 write new frm from alter table

git-svn-id: file:///svn/mysql.com/mariadb-5.5.30@54894 c7de825b-a66e-492c-adef-691d508d4ae1
refs #6090 5.6 inplace alter table

git-svn-id: file:///svn/mysql.com/mariadb-5.5.30@54895 c7de825b-a66e-492c-adef-691d508d4ae1
#36 use copy of alter_info for inplace alter since mysql_prepare_create_table is not idempotent