... Unnecessary because transitively included.
But each .cpp file still includes its own .h file near the top to ensure
that it compiles indenendently, even if it is reincluded transitively later.
... except Audacity.h
This forces us to make each header contain all forward declarations or nested
headers that it requires, rather than depend on context.
This #ifdeffed out TEST_CARD is useful for javascript code that shows how a
theme will look, when applied to Audacity. With the code enabled, each
pixel of audacity is painted with a colour that encodes the location in
the theme image map that was used.
Net result - in javascript you can change any colour in the theme cache
and instantly see how Audacity will look.
100% transparent black was appearing as black. Now it appears as the background colour.
AButton backgrounds now support alpha channel, which they did not before.
