accesslib:cleanup_contexts() - Fix invalid SQL syntax and reserved keywords
cleanup_contexts() was not working on Oracle - mostly due to 2 SQL
syntax problems. So probably marginally working elsewhere.
- We should not use AS when naming table/subselect aliases - only
when referring to column aliases in the resultset
- level is a reserved word - oops! - so back to contextlevel
This was breaking upgrades to 1.9 on Oracle.