* pythonmain.c: -k option, usage message, more environment flags.

(the latter also in frozenmain.c)
* ceval.c: global 'killprint' flag raises exception when printing an
  expression statement's value (useful for finding stray output)
* timemodule.c: add asctime() and ctime().  Change julian date to
  1-based origin (as intended and documented).
* Removed unused DO_TIMES stuff from timemodule.c.  Added 'epoch' and
  'day0' globals (year where time.time() == 0 and day of the week the
  epoch started).