roslyn: "Primary reference cannot be resolved" when referencing netstandard PCL from profle-based PCL

New PCL, Target .NET Standard 1.0 New PCL, Windows 8.1/.NET 4.5

Add a P2P ref to the first project from the second and build.

C:\Program Files (x86)\MSBuild\14.0\bin\Microsoft.Common.CurrentVersion.targets(1820,5): warning MSB3274: The primary reference "c:\users\rchande\documents\visual studio 2015\Projects\ClassLibrary13\ClassLibrary1\bin\Debug\ClassLibrary1.dll" could not be resolved because it was built against the ".NETPortable,Version=v5.0" framework. This is a higher version than the currently targeted framework ".NETPortable,Version=v4.5,Profile=Profile7"