daemon: do not leak resources

Before this patch, the client was responsible for removing FIFOs before
connecting. That left a whole bunch of FIFOs in the SuperUser /dev/...
directory. After This patch, the daemon removes FIFOs as soon as the client is
connected. (This is detected by making the daemon read from the control socket.)

This patch becomes unnecessary when file descriptors can be passed though
processes.
Merge pull request #206 from Lekensteyn/fix-resource-leaks

daemon: do not leak resources