Composite geometries end up with nested BBOX caches

[strk]

In 1.5 only the bbox of the outermost geometry was stored. In 2.0 it seems we're having the box also in the inner:

=# select st_summary('MULTIPOINT(0 0)'::geometry);
          st_summary           
-------------------------------
 MultiPoint[B] with 1 elements
   Point[B]

[pramsey]

OK, we get sensible results from ST_Summary now at r8076. Now to track down this extra [B]

[pramsey]

OK, the flags are now consistent with reality, which is an improvement. r8078