"real" table fails in JOINs".

This is a regression caused by the fix for Bug 18444. 
This fix removed the assignment of empty_c_string to table->db performed 
in add_table_to_list, as neither me nor anyone else knew what it was 
there for. Now we know it and it's covered with tests: the only case 
when a table database name can be empty is when the table is a derived 
table. The fix puts the assignment back but makes it a bit more explicit.

Additionally, finally drop sp.result.orig which was checked in by mistake.