[geos-devel] fastunion aggregate

[strk]

I've made a fastunion() aggregate working in a collect/union
way as explained in previous messages. 

Process size does not grow more then with plain unite() use.
It is actually the contrary: it keeps slightly smaller.
I think this is due to geomunion not releasing as soon as possible
detoasted arguments, but I did not check that yet.

Running speed is about 25% higher on a table of 191 geometries
organized in 20 records. Most of the time is spent in the finalfunc
and time spent grows with a rapid curve at each iteration.

If 'fastunion' is a good name for you I'll commit, so we can test
togheter. 

-strk;