bf75fe9d64
No real changes, just don't redeclare the classes already forward
declared in wx/bitmap.h in the files included (only) from it and don't
include redundant headers.
Also forward declare wxCursor and wxPixelDataBase in wx/bitmap.h itself
for consistency, as many (even though not all) headers use them.
Do not forward declare wxControl in wx/{msw,osx}/bitmap.h, however,
there is no reason to do it in this header.