Remove support and special handling code for Py3.2.

Try to include some more test dependencies in the travis build (but exclude them in Py2.6, which is often no longer supported already).

Include PySet_Check and PyFrozenSet_Check to CPython includes file

Repair some issues with coroutine exception handling

Disable refnanny in PyPy since it otherwise risks to access partly initialised objects, e.g. tuples.

Only reset the frame backlink of *internally* created exception tracebacks in generators/coroutines, not the ones stored away from the caller state.

Also make some C function signatures generic to avoid a dependency on concrete struct types in "far away" code.

This means abs(MIN_INT) has the "overflow" behavior of returning
MIN_INT as in C, but avoids surprising unsigned arithmetic for all
other values.

To preserve Python compatibility, abs(x) dissallows integer inference
for x just like the other potentially overflowing arithmetic operators.

This fixes Github Issue #1837