Rewrite the nio Pipe to use a Unix pipe behind the scenes.

We were using an AF_INET or AF_INET6 socket to implement the nio Pipe, which
was causing trouble for people on systems where IPv6 wasn't working yet.

This patch switches over to pipe(2). My first implementation used socketpair(2)
and retained the SocketChannelImpls, but it still seemed a bit off to be asking
for a full-duplex pipe to implement a unidirectional channel, and it required
hacks in the networking code to cope with the AF_LOCAL family, and in the
BlockGuard for the isLingeringSocket test.

This implementation uses pipe(2) and FileChannelImpl. It breaks a few tests, but
the tests are wrong, and it actually brings us closer to the RI's behavior of
throwing IOException "broken pipe" when writing to a broken pipe.

Rather than keep throwing junk into the FileSystem/NetworkSystem classes, and
resolving the question of which of those setNonBlocking belonged in (answer:
neither; this is a false Windows-style dichotomy that isn't helpful here), I've
added a new IoUtils with a few generally useful methods. The remainder of this
patch switches over existing code. We could probably make
FileDescriptor.descriptor private now I've exposed accessors, but this change
is large enough already...

Bug: 2735373
Bug: http://code.google.com/p/android/issues/detail?id=9431
Change-Id: I6b6d1e50bdddd435e71c31105a73c9d4fd135d7e
20 files changed