unix/main: Implement -m option for packages.

[pfalcon]

No description provided.

[pfalcon]

Something which was in technical debt for a while. Works pretty much like CPython, couldn't spot a difference in my testing ;-).

[dpgeorge]

Looks ok, but I didn't test it.

[pfalcon]

Travis build failure is due to extra condition added to builtinimport.c and minimal port code size increase due to that.

[pfalcon]

MSVC strikes again with C99 non-compliance with varlen arrays, switching to use alloca().

[pfalcon]

Actually, as usual, vstr_t ends up being used.

[pfalcon]

Looks ok, but I didn't test it.

This was mostly to review code patterns used, and well, I had to rewrite it with vstr_t in the end. I pondered about how to implement it and tested well enough, so merging. Maybe we should think how to integrate such command line params tests for unix port into coverage build.

[pfalcon]

Merged in edc02bd.

[dpgeorge]

Maybe we should think how to integrate such command line params tests for unix port into coverage build.

The mechanisms should be there in the cmdline/ tests.