Filter out net45 dependencies when you have a net40 package

Testing [redacted] and we have a number of packages which ship both net40 and net45 versions:

 - Caliburn.Micro
 - ReactiveUI.*
 - Rx.*

This becomes a problem on install because:

 - it will overwrite net40 versions of assemblies with net45 versions
 - it will introduce new net45 binaries, and likely more ReflectionTypeLoadExceptions (yay)

This change adds a couple of test scenarios (using Caliburn.Micro as the dependency) to ensure the release package is created correctly.

TODO:

 - [ ] ~~skip all the "portable-net45+*" profiles for a net40 app?~~ ignoring this for now