py: Raise TypeError when trying to format non-int with %x,%o,%X.

This behaviour follows Python 3.5 standard (in 3.4 it's a
DeprecationWarning which we'd rather make a TypeError).
modgc: Implement return value for gc.collect(), enable on Unix.
Figure out the test_name before using it (significant only to Travis skips)
Turn the Travis CI test skipping mechanism into something more generic
modgc: 64-bit cleanness.
modgc: Real 64-bit cleanness.
Fix str.modulo when precision is specified.
Merge pull request #668 from dhylands/print-prec

Fix str.modulo when precision is specified.
Merge pull request #667 from Rosuav/testfixes

A couple of small fixes to run-tests
objint: Fix corner case in buffer access.