[THEME] Export mcTheme_Initialize() and mcTheme_Terminate().
[MAKEFILE] MCTRL.DLL depends also on mCtrl.def.
[THEME] Make UXTHEME's function poitners global.
[MISC] Optimize mc_doublebuffer().

Whenever possible, use UXTHEME's buffered paint functions. Those use
cached bitmaps and DC's, leading to better performence when available.

Also updated relvant controls to call mcBufferedPaintInit() and UnInit()
to fully use it.