msvc: Use built-in alignof

This also fixes a 'unnamed type definition in parentheses' warning on the
alignof implementation define in binary.c
py: Fix mult by negative number of tuple, list, str, bytes.

Multiplication of a tuple, list, str or bytes now yields an empty
sequence (instead of crashing).  Addresses issue #799

Also added ability to mult bytes on LHS by integer.
Merge pull request #798 from stinos/msvc-alignof

msvc: Use built-in alignof