uv_tcp_get{peer/sock}name and uv_ip{4/6}_name should accept first argument by const pointer

Aforementioned functions do not modify first argument in any way, so passing first argument by non-const pointer is not required. I'm developing my own C++11 wrapper around libuv and have to keep mutable private member variables to expose wrapper functions as const member functions due to this issue. I really hope that I have done all required changes for OSX. Do not have any machine to test them unfortunately.

I know that second commit's message exceeds 50 chars limit, but I do not see any way to fit it in without even more cryptic abbreviations :)