Made pcap-stdinc.h more readable.

Include "IP6_misc.h" for all targets. Use non-Posix names for all MSVC-versions.
Update pcap-stdinc.h

Use non-Posix names for all MSVC versions.
pcap_compile() fix for Win32

Entangled this Italian spaghetti: ensure wsockinit() is called once to initialise the g_PcapCompileCriticalSection crit-sect. DllMain() used to do it, but not anymore since that wouldn't work when using libpcap as a static library.
Fix for static-lib use

Ensure WSAStartup() is called only once. Initialise crit-section and remember the error-code. Added pcap_wsockinit().
Merge pull request #356 from gvanem/master

Win32 changes