Change back default allocator to pooled.

Motivation:

While porting some changes from 4.0 to 4.1 and master branch I changed the default allocator from pooled to unpooled by mistake. This should be reverted. The guilty commit is 4a3ef90381f343a457243d6e2eabac01e551315b.

Thanks to @blucas for spotting this.

Modifications:

Revert changes related to allocator.

Result:

Use the correct default allocator again.