(GH-615) Test for source code changes if ShouldDocumentSourceFiles is set
(GH-615) Test for source code changes if ShouldDocumentSourceFiles is set

When generating docs, Cake.Recipe should take into consideration whether
or not changes in the project source code should result in updating the docs.
This is especially important when building API documentation using Wyam.
cake-contrib/Cake.Recipe,cake-contrib/Cake.Recipe