A little fix for table prefixes

In v.1.63 (cvs), the query in the update function

db_query("DESC term_access 'grant_list'")

should become aware of table prefixes etc. (in 2 places).

db_query("DESC {term_access} 'grant_list'")

I was getting SQL warnings in a multi-site with prefixes and shared tables. This seems to fix it.