WL#9167 Index merge hints.

    INDEX_MERGE, NO_INDEX_MERGE hints are added to allow the user to
    control index merge behavior for the particular query without changing
    the optimizer switch.

    INDEX_MERGE hint:

       The hint forces the optimizer to use index merge for the specified
       table using the specified set of indexes. If no index is specified,
       all possible index combinations are considered by the optimizer and
       cheapest one is selected.

    NO_INDEX_MERGE hint:

       The hint disables index merge combinations that involve any of the
       specified indexes. If no index is specified, index merge is not
       allowed for the table.

Author: Sergey Glukhov

mysql-test/r/mysqld--help-notwin.result

@@ -1443,7 +1443,7 @@ performance-schema-consumer-global-instrumentation TRUE
 performance-schema-consumer-statements-digest TRUE
 performance-schema-consumer-thread-instrumentation TRUE
 performance-schema-digests-size -1
-performance-schema-error-size 1080
+performance-schema-error-size 1081
 performance-schema-events-stages-history-long-size -1
 performance-schema-events-stages-history-size -1
 performance-schema-events-statements-history-long-size -1

mysql-test/r/mysqld--help-win.result

@@ -1439,7 +1439,7 @@ performance-schema-consumer-global-instrumentation TRUE
 performance-schema-consumer-statements-digest TRUE
 performance-schema-consumer-thread-instrumentation TRUE
 performance-schema-digests-size -1
-performance-schema-error-size 1080
+performance-schema-error-size 1081
 performance-schema-events-stages-history-long-size -1
 performance-schema-events-stages-history-size -1
 performance-schema-events-statements-history-long-size -1