Auto merge of #300 - rrichardson:master, r=alexcrichton

added const SOCK_SEQPACKET,  and SOCK_RDM where applicable

... which is used for UNIX Seqpacket sockets as well as SCTP IP.

I have verified in source on  a couple Linux flavours as well as freebsd and darwin source that SOCK_SEQPACKET has value 5.
Solaris is the odd one with a value of 6.  I also added RDM for solaris (value 5)