swift234

Make -i compatible with shebangs and forward arguments correctly

The driver option -i now requires an input file as argument, and any
options after the input file will be treated as arguments to the
interpretted file.

This also renames the frontend option to -interpret, since it is parsed
as a flag, unlike -i. We could support -interpret in the driver if we
wanted, which would allow us to use --, but wouldn't work with shebang
scripts. For now, it's frontend-only.

Swift SVN r19718