[Matrix-SIG] Multipack requires 1.5.2b2 or later

[Travis Oliphant]

The Multipack package I discussed a couple of days ago requires 1.5.2b2 or
later to run.  The reason is that it makes use of the "N" option to
Py_BuildValue in the C/API of Python that was added at the 1.5.2b2 stage.

I'm sorry if neglecting to mention this wasted your time.  It is not hard
to fix the code for other (previous) versions by replacing the N with an
O.  This will, however, create a memory leak in Python as the array
objects returned will have a double reference count increase.  (That's why
I used "N" in the first place.  I didn't know it was a "recently-added"
feature.)

I suspect people who will be using Multipack will be getting 1.5.2 anyway?
If there is a real demand for functionality with 1.5.2b1 and before, it is
not hard to change the code to make it work.  

Let me know.

Travis