rel_project2groupby never actually changes is second parameter, so the extra indirection is not needed.
rel_project2groupby never actually changes is second parameter, so the
extra indirection is not needed.

In rel_aggr, there was no assignment to either rel, *rel, or old
between the assignment old = *rel and the check whether old != *rel,
so we don't need old.

Also in rel_aggr, if the call to rel_project2groupby returns NULL, we
can rel_destroy the original *rel argument (since *rel was overwritten
with NULL, that relation is not needed anymore).

The sql tests run no worse than before these changes.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb