General:
*         Upgraded Steamworks SDK to v1.29
*         Fixed mod compatibility problem with Multiplayer Base that was introduced in September.
*         In Hammer, while using the Vertex Tool, pressing CTRL+B will snap selected vertices to the grid.

Virtual Reality:
*         Mods that support virtual reality now need to have a line in gameinfo.txt that says “supportsvr 1”. This indicates to gameui and engine that certain UI should be enabled.
*         VR-enabled mods will now start up in VR mode when launched from Steam’s VR mode.

Windows:
*         Upgraded to Visual Studio 2013. If you need to build projects for VS 2010, add /2010 to your VPC command line.

OSX:
*         Upgraded to XCode 5.
Merge branch 'master' of https://github.com/ValveSoftware/source-sdk-2013
Added VS2010 version of libprotobuf for folks who are still using VS2010
* Added support for Visual C++ 2013 Express to VPC
* Added support for running VPC on Windows XP
Updated the SDK with the latest code from the TF and HL2 branches.
Merge remote-tracking branch 'upstream/master'

To ensure that compatibility remains between the VIGoV project and the actual Source SDK base that's running it.
Added some complex number stuff to the mathlib, more to come...
Merge branch 'master' into fixed - as you can probably guess, the master is broken, so this "ours" merge is being done to get rid of it