check for XXXApp_8C.html (Application) in the -doc argument handling first.

This is useful when the application has the same name as a class. For example,
polyDualMeshApp.C implements the polyDualMesh application using the
polyDualMesh class. Thus polyDualMeshApp_8C.html documents the app, whereas
polyDualMesh_8C.html is the annotated source code for the class itself.