Fix #34 correct checksum caculation when IPv6 extension headers being used
Insource comments and whitespace cleanups
Merge pull request #36 from sam-github/fix-ip6-checksum

Fix ip6 checksum
Fix build error in Mac OS X

The IFT_FASTETHER, IFT_FASTETHERFX, IFT_GIGABITETHERNET constants are not defined in Mac OS X Mountain Lion. Only IFT_ETHER and IFT_L2VLAN are. This patch checks for the existence of these definitions.
Factorize socket setup code for socket opening

This patch is factorizing the socket opening code between IPv4 and IPv6.
Socket option are the same for IPv4 and IPv6, so we can factorize the code.
As a side effect this patch brings output device selection to IPv4.
Fix errors with missing IPPROTO_MH on windows

Use of IPPROTO_MH was introduced with a89f0f10de, but definition
was conditionalized to non-windows platforms.
For samples, netinet/in.h is not on windows
Remove obsolete SYMBOL_CACHE_SIZE from doxygen.conf
Prepare for 1.2 release candidate 3
Reset global cq state after destroying it
Fix error in win32 get_ipaddr4 causing buf overrun

In libnet_get_ipaddr4 (__WIN32__ defined) the
PacketGetNetInfoEx(l->device, &ipbuff, &npflen) takes a pointer to the
count of buffers in the last parameter, not to the size of one buffer.
This causes buffer overruns (tested in MSVC 2013 ultimate), changing the
npflen to 1 solves this issue.
Support musl libc, remove support for glibc < 2.1

The workarounds for glibc < 2.1 (was released february 1999) break the
build with musl libc.

It is very unlikely that 2.0 or earlier is still in use, and if so,
1) that's a big security hole
2) code wouldnt compile anyway since noone tested build in the last decade
3) user of it wouldn't expect anyway to get bleeding edge sw built on it,
   so he would just use the latest version that works for him.

Closes #52