Update gyp for VS 2013 support, simplify configure logic to rely on gyp for detecting visual studio

Gyp has recently added a number of fixes to support the release of Visual Studio 2013.  These are important changes because finding older versions of Visual Studio Express can be difficult and this is causing many issues for our Windows users of Node.

This patch brings in the minimum update -- the appropriate files from the latest Gyp code and removal of duplicative logic for detecting/selecting Visual Studio versions inside lib/configure.js.