Previously we were just using Prelude's `readFile`, which uses the
system default locale. This meant that people writing Cryptol in other
locales might produce source files that work fine for them but not
others. Now the interpreter sets the default locale to utf8 at startup.
Additionally, the code to catch exceptions from loading modules was too
lazy, allowing exceptions to bring down the whole process when the
module contents were forced outside of the `try`.
We also assumed that any IO exception was from files not being found;
there's now an "Other IO exception" possiblity. Incorrect locales will
trigger this alternative because the actual IOException raised isn't
specific to locale errors.
