This patch adds a counting of the number of allocated memory blocks (through the PyObject_Malloc API). Together with -R, it can help chase those memory leaks which aren't reference leaks (see c6dafa2e2594).

The sys.getallocedblocks() function is also available in non-debug mode. This is meant to help 3rd party extension writers, who rarely have access to debug builds.

To avoid too many false positives, issue13389 is a prerequisite (at least for the "test -R" part of the patch). Even after it, there are still a couple "test -R" failures; we'd have to investigate them.