Handle --print-exception-stacktrace and --version more elegantly.

Review Request #1871 — Created March 6, 2015 and submitted — Latest diff uploaded

jinfeng, jsirois, patricklaw, zundel
- --print-exception-stacktrace is now a regular global option.
  Previously it was registered as one, but not actually used.
  Instead, pants_exe.py special-cased it by looking for it on the
  cmd line. This meant that it couldn't be set in config, for example.

- --version is now special-cased in the options parser, using the same
  mechanism as --help. This makes sense as --version is very similar
  to --help in spirit, and isn't really an option (you'd never want
  to set it in config, for example).

- --log-exit support was removed, since it doesn't currently work, and
  is completely unnecessary anyway.

CI passes: https://travis-ci.org/pantsbuild/pants/builds/53283617

Manually tried the various flags.