[libbase] minor apple fixes
[libbase] cmake: adds checks for splice() and tee()
[libbase] Pipe: adds copy(pipe, len) method to duplicate data from a pipe to a pipe.
[libbase] Pipe: some documentation plus a fix in pipe.write(socket, n)
Merge commit '3ec23261f59156477f8b8cbfeb62484a88ddc6de'