iPhone compatibility fix and demo app

[Jens Alfke]

I fixed a glitch in an #ifdef that was keeping TCPConnection.m from
building for iPhone OS.
I also added an example Xcode project that builds a trivial iPhone app
— all it does is run the BLIP echo server and display its current
status on the screen. You can run the echo client on a Mac and talk to
it.

Note that when using MYNetwork in an iPhone app, you have to add
CFNetwork.framework to the target. I think this may have been the
cause of the link errors some people reported.

—Jens