Print mypy version on error

[pkch]

Is it worth printing version number on INTERNAL ERROR? If so, we can use this small patch to do so.

I also added INTERNAL ERROR output at the outer level (mypy.main) in case we don't catch it inside; it happened for example in #3232.

[gvanrossum]

I like the idea of printing the version on internal errors. I do not like the complexity of calling report_internal_error() from the main script.

[pkch]

I just push --force a simpler commit that just prints mypy version, and doesn't do anything else. Didn't mean to close it, I think it's some weird github logic :)

Edit: nm, I forgot to commit and so push --force the current master haha