Don't use double buffering on platforms that do it automatically.

Don't use double buffering on platforms that do it automatically.

Filters out unrecognised keycodes in OnChar, and added numeric
keypad navigation keycodes.

Added SetStyleEx which takes flags for specifying option such
as optimization (only apply necessary styles), char/para style
only, and use undo. Used SetStyleEx when applying styles to
avoid applying character styles to paragraph objects, and vice versa.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41705 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775