fix VS 2008 project file generation

Commit 4f21eb03

 utterly broke the project file generation for
VS 2008. The introduced filterByName convenience methods looks for
filter names like "Generated Files", but the code path for
VS <= 2008 used filter names like "GeneratedFiles".
The generated projects were valid but empty.
This commit ensures that both VS generators use the same filter
names.

Task-number: QTBUG-41821
Change-Id: I828fa911bae8d835b073a4c2260316127cc72cda
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>