fix multiple change to csprojfile with some pkg

[kYann]

When using a package that include another dll in his lib folder. And the
other dll exists as a package, then csprojfile are changed multiple
times du to addassemblies save. In that case we have a reload all window
on vs.

Package creating conflicts :

• TweetSharp-Unofficial (embed hammock and newtonsoftjson)

To reproduce the issue, install TweetSharp-Unofficial then newtonsoftjson (or hammock) in project.
You'll see the csproj file wirte change every time the task FixReferences is runned.

[jmarnold]

Because I'm being lazy, what's the fix do exactly? How do you determine which one should be added?

[kYann]

The first found occurence of the assembly name wins (for the current project being "fix").
I don't know if there is a better way to choose which one should be keeped.