test: remove 'is root?' check

I debug tests regularly as root (because dtrace and dtruss require the
additional privileges). The 'is root?' check gets in the way more often
than it prevents me from doing something silly. Remove it.
unix: make stream.c internal functions static
darwin: fix read from uninitialized struct kevent

In the OS X fallback code, don't read from the struct when the kevent()
syscall times out.
build: make clean target remove all build artifacts
build: add distclean target to out-of-tree builds