first load them to the data dictionary cache and use the normal
routines for dropping tables or indexes.  This should reduce the
risk of bugs and also make the code compatible with the upcoming
TablespaceDictionary implementation.

DICT_SYS_INDEXES_NAME_FIELD: The clustered index position of SYS_INDEXES.NAME.

row_merge_drop_temp_indexes(): Scan SYS_INDEXES for tables containing
temporary indexes, and load the tables as needed. Invoke
row_merge_drop_index() to drop the indexes.

row_mysql_drop_temp_tables(): Scan SYS_TABLES for temporary tables,
load them with dict_load_table() and drop them with
row_drop_table_for_mysql().

rb://251, not yet reviewed