Fix for multiple files with the same name.

[akb825]

When multiple files with the same filename, but different path, appear
in the same solution, all files will be displayed. Duplicates of the
same file path will still be removed.

e.g. C:\Foo\Bar.h and C:\Baz\Bar.h will both be shown. However, if
C:\Foo\Bar.h is referenced twice it will only be shown once.

[akb825]

Sorry, I missed that the filename was being checked to remove duplicate items when adding the grid view. Now that Filename is just the filename portion rather than the full path, it caused files with the same name but different paths to be dropped.

[parnic]

Thanks for the fix!