[postgis-devel] collect() updated

[strk at refractions.net]

I've fixed the collect() aggregate so that it keeps input geometries
structure.
The function returns a GEOMETRYCOLLECTION if:
	any multi type is found in input
	OR
	different single types are found in input

Alternatively it can return a MULTI if:
	all input is SINGLE typed
	AND
	all input has the same type

The function *never* returns a single type (ie. POINT=>MULTIPOINT).
You can use force_multi() to obtain the MULTI version.
You can use force_collection() to obtain the COLLECTION version.

The memcollect() function has been obsoleted (does not actually save
much memory).

--strk;