Add warning mode for classic division, almost exactly as specified in PEP 238. Changes: - add a new flag variable Py_DivisionWarningFlag, declared in pydebug.h, defined in object.c, set in main.c, and used in {int,long,float,complex}object.c. When this flag is set, the classic division operator issues a DeprecationWarning message. - add a new API PyRun_SimpleStringFlags() to match PyRun_SimpleString(). The main() function calls this so that commands run with -c can also benefit from -Dnew. - While I was at it, I changed the usage message in main() somewhat: alphabetized the options, split it in *four* parts to fit in under 512 bytes (not that I still believe this is necessary -- doc strings elsewhere are much longer), and perhaps most visibly, don't display the full list of options on each command line error. Instead, the full list is only displayed when -h is used, and otherwise a brief reminder of -h is displayed. When -h is used, write to stdout so that you can do `python -h | more'. Notes: - I don't want to use the -W option to control whether the classic division warning is issued or not, because the machinery to decide whether to display the warning or not is very expensive (it involves calling into the warnings.py module). You can use -Werror to turn the warnings into exceptions though. - The -Dnew option doesn't select future division for all of the program -- only for the __main__ module. I don't know if I'll ever change this -- it would require changes to the .pyc file magic number to do it right, and a more global notion of compiler flags. - You can usefully combine -Dwarn and -Dnew: this gives the __main__ module new division, and warns about classic division everywhere else.