Visual Studio 2014 support for node v0.10.x series

Work in progress to get node v0.10.x working against Visual Studio 2014

 - [ ] figure out what changed with getenv/setenv behavior with 2014 runtimes (https://github.com/mapbox/node-srs/issues/48)
 - [ ] try to get gyp 2014 patch accepted upstream - https://code.google.com/p/gyp/issues/detail?id=446&q=2014


Okay - thinking about trying to get this upstream eventually - maybe we could switch to using `C:\Program Files (x86)\Windows Kits\8.1\bin\x64\ctrpp.exe` only if it exists and falling back to `C:\Program Files (x86)\Windows Kits\8.1\bin\ctrpp.exe`? I presume that >= 2014 uses the arch folder but not previous versions?