Revert "Also disable MarkAsDirty that otherwise marks the projects to be save needy"

This reverts commit e42e1e40ec2cf059d9020d151aae5cf402c77dbb.
Really fixed sprurious projects marked dirty. Invalidate projects when really needed.

Previous fix was wrong. Keeping the add/remove property trick, the fix was
savin g properly the project when initially marked as not dirty.  We also invalidate
projects when it's really needed, detecting the state project configuration is unchanged when switching solution configuration.
Fix really scan all projects

Iterating _DTE2.Solution.Projects is not enough. Added some extension
methods to allow full iterations through solution tree
Missing Extension.cs file in VS2010 project
Bump to version 1.0.2
Updated changelog