unix: fix missing return value warning in stream.c
build: serial-tests was added in automake v1.12

Commit a97685e added a check that tries to ascertain whether the
serial-tests option is supported by automake. It assumed that said
option was added in automake v1.11 but it turns out that's wrong, it
wasn't added until v1.12. Update the check.

Of course, none of this would have been necessary if the automake people
had simply added a macro that tells you if serial-tests is supported or
not.
windows: fix uninitialized local variable warning

Pass the user-returned buffer to the read calback. Fixes the following
warning:

    src\win\tcp.c(439): warning C4700: uninitialized local variable
    'buf'
windows: fix missing return value warning

Fixes the following warning:

    src\uv-common.c(476): warning C4715:
    'uv__getaddrinfo_translate_error' : not all control paths return
    a value

The function never returns - the final statement is a call to abort() -
but it seems MSVC's program flow analyzer is too weak to figure that
out.