Forbid creation of wxPaintEvent objects from user code

This doesn't work anyhow, so it's better to prevent the code doing this
from compiling instead of getting run-time asserts or worse.

Also simplify construction of these events inside wxWidgets by passing
the window itself to the ctor instead of passing just its ID and calling
SetEventObject() separately later.

For consistency, do the same thing for wxNcPaintEvent too.

docs/changes.txt

@@ -103,6 +103,10 @@ Changes in behaviour which may result in build errors
   then you will need to add these libraries to your make or project files
   yourself.
 
+- wxPaintEvent objects can no longer be created by the application code. This
+  was never supposed to work and is now forbidden at compile-time instead of
+  resulting in errors during run-time.
+
 - WXWIN_OS_DESCRIPTION doesn't exist any longer, use wxGetOsDescription().
 
 - Never documented and not always available private wxGetClipboardData()