[MDITAB] Implement MC_MTM_ENSUREVISIBLE.

Changing selected item also ensure the item is visible.
[MISC] mc_clip_set(): Fix off-by-one pixel bug.
[THEME] Fix buildability under MSVC.

MS SDK does not define type "PROPERTYORIGIN", only "enum PROPERTYORIGIN".
[VS2010] Add project for example ex_treelist2.
Bump version to 0.9.1
[THEME] Fix bogus gcc warning about potentially unsed variable.
[THEME] Fix copy&paste errors in documentation.
[MDITAB] Fix ScrollWindowEx() artifacts.
[Makefile] Get rid of linker warnings about stdcall fixup.