combined lr-wpan patch from Margherita and Sascha

This patch was posted to ns-developers on January 23:
http://mailman.isi.edu/pipermail/ns-developers/2014-January/011692.html

The main features implemented by the first patch are:
* Support for ACKs
* Only a single packet can be received at once. The first packet with a signal power higher than the receiver sensitivity is completely received, while packets arriving during reception of a packet are always dropped. No interference modelling.
* Fixed bug https://www.nsnam.org/bugzilla/show_bug.cgi?id=1775
* Switching the transceiver state takes aTurnaround time
* 6LoWPAN support in NetDevice
* Removed some bugs in the PHY and MAC

The main features of the second patch are the version 1 patch sent by Sascha on 23.01.2014 plus (Sascha's comments below pasted in):
 + Fixes for compiler errors in tests and examples.
   - I didn't test the examples.
   - There are no current tests for the new code.
 + clang and icpc fixes.
 + Many code cleanups.
   - Mostly removing unnecessary includes.
   - Removal of unused source files.
 + Bug fix for the MAC "state machine" in conjunction with pending ACKs.
   - If a regular packet is received while waiting for an ACK, the ACK
     is considered as lost.
 + Feature patch of Erwan Livolant for FCS calculation
   - I changed the patch slightly to enable FCS calculation and
     verification only when the global attribute ChecksumEnable
     is set, like it is done in the csma module.

[Tommaso Pecorella, 2014-02-11 19:33:33]

https://codereview.appspot.com/59240044/diff/1/src/lr-wpan/helper/lr-wpan-hel...
File src/lr-wpan/helper/lr-wpan-helper.cc (right):

https://codereview.appspot.com/59240044/diff/1/src/lr-wpan/helper/lr-wpan-hel...
src/lr-wpan/helper/lr-wpan-helper.cc:26: #include <ns3/mobility-model.h>
I don't think this is necessary.

https://codereview.appspot.com/59240044/diff/1/src/lr-wpan/model/lr-wpan-mac-...
File src/lr-wpan/model/lr-wpan-mac-header.h (right):

https://codereview.appspot.com/59240044/diff/1/src/lr-wpan/model/lr-wpan-mac-...
src/lr-wpan/model/lr-wpan-mac-header.h:45: #include <ns3/mac64-address.h>
These are "", as they're not system-wide.

Also, check the includes in the other files as well.