Working print command with uzblctrl

Working print command with uzblctrl

Also: Changed a few g_error to g_warning to avoid crashes on broken
socket. Flush the channel after sending, shutdown before closing.
Removed unused headers from uzblctrl.c.

The socket protocol is straightforward: you send a command terminated
with a newline, you receive a reply terminated with a newline.
If you ever need newlines inside a reply, you'll have to change this.

uzblctrl closes the connection after getting the reply, but any other
client can stay connected and send/receive other commands.