Refactor assertion checking of StampAssemblyTests

Doing it this way displays the expected and actual text if a test fails,
making it easier to see what's wrong.
Enhance assembly stamping

- support AssemblyInformationalVersion
- allow to use hash code in AssemblyInformationalVersion. This works
  since that is treated as a string by the framework.
- some refactorings

Change-Id: I939b1f12234c313cd6e3db3f555dafad48a9f843
Merge pull request #98 from ermshiperete/feature/EnhanceStamping

 Enhance assembly stamping