Make command-line Python scripts more convenient
Overhaul tests

Add more details of files needed for tests

Add some files that are missing but can be put into git (i.e. are
suitably licensed)

Improve test descriptions
python.html: small improvements
Revert "Require Python >= 3"

This reverts commit e4b0c7fbdeef4f201bf10a6193ed8385069eae31.
Add missing includes of progname.h for set_program_name

Mingwin doesn't support GC_set_handle_fork, so #ifdef around it.
Require Python >= 2.6

Fix warnings and remove dead code from python.c

Common up Python 2 & 3 code using macros (thanks, @mhosken)