Fix DataThread memory leaks.

Make DataThread::~DataThread() virtual so subclass destructors get
called.

Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>
Add empty UDPReaderThread files.

These will contain a DataThread for reading from a UDP socket.

Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>
[NOMERGE,WIP] Add UDPReaderThread implementation.

TODO:

- think of a testing strategy
- debug on Linux
- test on OS X
- add hooks for Windows
Teach SourceNode, ProcessorList, ProcessorGraph about UDPReaderThread.

Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>
ProcessorList.cpp: astyle.

Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>