Reimplement NdrSimpleTypeUnmarshall using similar macros to
NdrBaseTypeUnmarshalling without buffer checks, due to
NdrSimpleTypeUnmarshall not doing any safety checks.

Use RegInstall instead of RegInstallA as RegInstallA isn't available in
some native versions of advpack commonly installed by programs.

user32: Make sure there is space for at least 6 items in a combo dropdown without forcing it to be at most 6 items as well.

imm32: Remember to unset the hwnd for a context when that hwnd is associated with a different context.

Mostly NOP regarding existing functionality, but makes it possible to skip light 
activation when it's not needed (like when clearing).