GYP_MSVS_VERSION=2013 ignored when other versions of VS are installed

[GoogleCodeExporter]

What steps will reproduce the problem?
0. Have Visual Studio 2013 as well as Visual Studio 2010 installed (I also had 
VS2012 installed but I don't know if this also comes into account)
1. set GYP_MSVS_VERSIONS=2013
2. generate the project

What is the expected output? What do you see instead?
The first two lines of build.ninja shuld look like this (using VS2013 
executables):
cl_x86 = "C:\Program Files (x86)\Microsoft Visual Studio 
12.0\VC\bin\amd64_x86\cl.exe"
cl_x64 = "C:\Program Files (x86)\Microsoft Visual Studio 
12.0\VC\bin\amd64\cl.exe"
So that ninja compiles uses the VS2013 compiler

Instead, they look like this :
cl_x86 = "C:\Program Files (x86)\Microsoft Visual Studio 
10.0\VC\bin\amd64_x86\cl.exe"
cl_x64 = "C:\Program Files (x86)\Microsoft Visual Studio 
10.0\VC\bin\amd64\cl.exe"
So ninja compiles with the VS2010 compiler

What version of the product are you using? On what operating system?
Using the gyp version retrieved by the cef3 trunk automate script
Windows 8, Visual Studio 2013 Ultimate, VS2010 Ultimate, VS2012 Ultimate

Please provide any additional information below.
By uninstalling any version of Visual Studio other than 2013 and running the 
steps again, I got the good result.

Original issue reported on code.google.com by benjamin...@aerys.in on 22 Jan 2014 at 11:09

[GoogleCodeExporter]

Please let me know if this issue is accepted, I'd be happy to take a pass at 
creating a fix.

Original comment by j...@hikinghomeschoolers.org on 15 Feb 2014 at 8:20

[GoogleCodeExporter]

I have the same issue.  It is using the wrong visual studio when VS2010 and 
VS2013 are installed.

Original comment by l...@unity3d.com on 20 May 2014 at 1:30