Moved some stuff here from main.c (part of a big restructuring - wait

for more!).

- The global flags that can be set from environment variables are now
set in Py_Initialize (except the silly Py_SuppressPrint, which no
longer exists).  This saves duplicate code in frozenmain.c and main.c.

- Py_GetProgramName() is now here; added Py_SetProgramName().  An
embedding program should no longer provide Py_GetProgramName(),
instead it should call Py_SetProgramName() *before* calling
Py_Initialize().