1. wxSpinButton fixed: it now sends EVT_SPIN_UP/DOWN messages (and unnecessary

1. wxSpinButton fixed: it now sends EVT_SPIN_UP/DOWN messages (and unnecessary
   old code which didn't send them anyhow removed). It also allows to veto the
   changes, but this feature is not portable and as such is not documented.
2. wxBitmapBuuton doesn't lose its bitmap any more
3. wxImage::ConvertToBitmap() doesn't crash if image is !Ok() but just
   returns wxNullBitmap.
4. wxProgressDialog looks much nicer under Windows and its estimated/elapsed/
   remaining time fields actually show some non random numbers now
5. MDI client window doesn't flicker because wxMDIParentFrame doesn't position
   it at (0, 0) first before moving it to correct location
6. other minor fixes...

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@3181 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775