Only _WIN32 is defined by the compiler, and WIN32 is not standardized
and may be missing.

Closes #169

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

Signed-off-by: Lazaros Koromilas <lostd@2f30.org>

Haiku has struct ucred but no SO_PASSCRED (yet).

The implicit cast operator can be very dangerous.

Fixes build failure because Bionic doesn't provide SUN_LEN().

For improved portability of the net library to projects without
autoconf.

Use wchar_t for everything on Windows.  Solves a lot of filesystem
charset problems.

Handles abstract sockets on Linux.