PROBLEM AFTER MYSQL_HA_FIND

This problem occured if a prepared statement tried to create a table
for which there already existed a view with the same name while a
SQL handler was opened.

Before DDL statements are executed, mysql_ha_rm_tables() is called
to remove any matching tables from the internal list of opened SQL
handler tables. This match was done on TABLE_LIST::db and 
TABLE_LIST::table_name. This is problematic for views (which use
TABLE_LIST::view_db and TABLE_LIST::view_name) and anonymous
derived tables.

This patch fixes the problem by skipping TABLE_LISTs representing
anonymous derived tables and using get_db_name()/get_table_name()
which handles views when looking for SQL handler tables to remove.