Msg.d

Added POSIX wrapper for <sys/msg.h>

I asked for help on this link: http://forum.dlang.org/thread/lradkwgmyotmldzhynrc@forum.dlang.org and was advised to do a pull request.  This is my first pull request. 
Added necessary changes into latest commit. Since I was unable to find specific for X86_64 I used those for X86. Actually all these versions used unsigned long int; none, at least to my knowledge, used different type.