IE completely broken in master

[mramato]

Run Cesium Viewer in IE and you'll get the below error. This does not happen in 1.4

RuntimeError: Vertex shader failed to compile.  Compile log: Shader compilation errors
(0, 0): Function 'get2DYPositionFraction' is declared and used but not defined

Error
   at RuntimeError (http://localhost:8080/Source/Core/RuntimeError.js:42:13)
   at createAndLinkProgram (http://localhost:8080/Source/Renderer/ShaderProgram.js:503:17)
   at initialize (http://localhost:8080/Source/Renderer/ShaderProgram.js:689:9)
   at ShaderProgram.prototype._bind (http://localhost:8080/Source/Renderer/ShaderProgram.js:706:9)
   at beginDraw (http://localhost:8080/Source/Renderer/Context.js:1793:9)
   at Context.prototype.draw (http://localhost:8080/Source/Renderer/Context.js:1860:9)
   at DrawCommand.prototype.execute (http://localhost:8080/Source/Renderer/DrawCommand.js:185:9)
   at executeCommand (http://localhost:8080/Source/Scene/Scene.js:1050:13)
   at executeCommands (http://localhost:8080/Source/Scene/Scene.js:1279:17)
   at render (http://localhost:8080/Source/Scene/Scene.js:1377:9)

[kring]

That has to be from #2346, though I don't know why it would only show up on IE. I'll take a look soon.