clsToolTip: add special check for new radio button implementation
pdFont: remove superfluous functions, make DC interactions more intelligent
Radio button UC: rebuilt from the ground up

See comments for details.

PD's radio button control was one of the first UCs I ever built.  As
such, it had a lot of dumb implementation details.  Back then, I also
lacked a lot of crucial supporting code - like GDI+ interfaces and a
dedicated font class - so the old control was only marginally better
than VB's internal version.

I hadn't intended to tackle a full rewrite prior to 6.4's release, but
I'm itching to get cracking on Unicode stuff, and this was a low-impact
blocker with immediate benefits.  Also, with the new slider control
being added in 6.4, it's probably not a bad idea to unify a few other UI
elements alongside it.

The new control has much, much cleaner implementation than the old one.
It's completely owner-drawn, and it's ready for Unicode support thanks
to custom text rendering via pdFont.

There's still quite a bit of refinement to-do (e.g. testing on XP and
high-DPI Win 8 hasn't happened yet), but as the new implementation is
completely functional on Win 7 100% DPI, this is a good time to take a
snapshot.