simplify MSBuild defaulting logic according to code review
simplify MSBuild defaulting logic according to code review

dkinitiate/VisualFSharpPowerTools,isaacabraham/VisualFSharpPowerTools,forki/FSharpVSPowerTools,vasily-kirichenko/FSharpVSPowerTools,fsprojects/VisualFSharpPowerTools,smoothdeveloper/VisualFSharpPowerTools,yever/VisualFSharpPowerTools,cloudRoutine/VisualFSharpPowerTools,dungpa/PowerTools,fsprojects/VisualFSharpPowerTools,vasily-kirichenko/FSharpVSPowerTools,cloudRoutine/VisualFSharpPowerTools