restore should support multiple project files targeting same baseintermediateobjdir

[niemyjski]

I'm running the latest VS2017 release and dotnet 1.0.0 on windows 10 x64 stable. I came across a potential bug with dotnet restore.

Here is the a link the source:
https://github.com/exceptionless/Exceptionless.Net/tree/9614d2bc1d2cb949945d05ff4dbf0d8bed0738f0

I have to have signed nuget packages so my initial goal was to have my shared library have a project.csproj and a project.signed.csproj in the same folder. Then in depending packages (projectc) have a msbuild condition based on the state of SignAssembly and reference the correct csproj file and set the new package id. This failed because dotnet restore creates the lock file without signing. So when I build projectc it works, when I do a second pass on projectc with a msbuild property set to enable signing it would compile the first signed target framework and then blow up with a crazy error. I have sense abandoned this approach and went for a new csproj and folder per signed project as I couldn't get around this.. I no longer have the error message but it should be simple to reproduce.

[nkolev92]

Duplicate of #4463