Ah, this is a fun one. Evidently on Py2.7, the parameters to `zlib.compressobj()` are positional *only* - passing them as kwargs (like `zlib.compressobj(wbits=24)`) throws `TypeError: compressobj() takes no keyword arguments`. So this is just a thin wrapper to paste over that strange deficiency that must have gotten fixed in Py3.0. I think I'll move it to `compat`, actually...