Add utun support for gogoCLIENT

With some copy and paste work, it’s working now.

Utun support: utun works like OpenBSD’s tun. We need to take care of the first 4 bytes. That’s all.
Openssl: Since El Capitan, openssl headers are removed. So, use macports’s headers.

Code is on github https://github.com/evi1c/gogoc/commit/bd9af4101ac6134c90b61b01c78d140f68bae25e

Ref:
https://github.com/mafintosh/utun
http://www.newosxbook.com/src.jl?tree=listings&file=17-15-utun.c#main
http://lists.unix-ag.uni-kl.de/pipermail/vpnc-devel/2014-October/004126.html
https://github.com/breiter/vpnc
http://sourceforge.net/p/openvpn/mailman/openvpn-devel/thread/51C2C433.9070402%40rfc2549.org/#msg31071812

% sw_vers
ProductName: Mac OS X
ProductVersion: 10.11
BuildVersion: 15A284

Build gogoc on OS X El Capitan

According to http://lists.apple.com/archives/macnetworkprog/2015/Jun/msg00025.html and test on OS X El Capitan with XCode 7.0.1, it’s not possible to build gogoc now. A quick fix for building this useful tiny utility, is to make use of macports. This is a quick hack. Need to do some research to¬†understand how people deal with OS X without openssl header files.

diff -ruN gogoc-1_2-RELEASE~/gogoc-tsp/Makefile gogoc-1_2-RELEASE/gogoc-tsp/Makefile
--- gogoc-1_2-RELEASE~/gogoc-tsp/Makefile	2010-03-08 03:49:54.000000000 +0800
+++ gogoc-1_2-RELEASE/gogoc-tsp/Makefile	2015-10-03 21:09:45.000000000 +0800
@@ -61,7 +61,7 @@
 	$(PWD)/conf \
 	$(PWD)/man
 
-CC_INC_PATHS=-I$(PLATFORM_DIR)/$(PLATFORM) -I$(PWD)/include -I$(GOGOCPAL_INCDIR) -I$(GOGOCPAL_DEFDIR) -I$(GOGOCCFG_INCDIR) -I$(GOGOCMSG_INCDIR)
+CC_INC_PATHS=-I$(PLATFORM_DIR)/$(PLATFORM) -I/opt/local/include -I$(PWD)/include -I$(GOGOCPAL_INCDIR) -I$(GOGOCPAL_DEFDIR) -I$(GOGOCCFG_INCDIR) -I$(GOGOCMSG_INCDIR)
 LD_LIB_PATHS=-L$(GOGOCPAL_LIBDIR) -L$(GOGOCCFG_LIBDIR) -L$(GOGOCMSG_LIBDIR)
 LD_LIBRARIES=-lgogocpal -lgogocconfig -lgogocmessaging

PS:
% sw_vers
ProductName: Mac OS X
ProductVersion: 10.11
BuildVersion: 15A284