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

Work in progress to get node v0.10.x working against Visual Studio 2014

 - [x] 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