Windows Build Errors After !355 (Refactor Message Digest and HMAC API)

In order to resolve the build errors caused by !355 (merged),

replace

#include <arpa/inet.h>

with

#ifndef WIN32
#include <arpa/inet.h>
#endif

in lib\dns\hmac_link.c

and add

<ClInclude Include="..\include\isc\md.h" />

<ClCompile Include="..\md.c" />

to lib\isc\win32\libisc.vcxproj.in