change default variants to qt4-* ?

[Michael Dickens]

I think my changes to the qt4-* series are almost stabilized; one reason
there have been so many issues is because Qt is so large in size and
takes so long to compile (~2 hours on my 2.6 GHz MacBook Pro) -- & hence
some changes were done by "winging it" (and, those I messed up were
certainly "my bad").  I added a "no_debug" variant since it turned out
to be simple, and there are already variants for "no_examples" and
"no_demos" ... but none are defaults -- the users has to specifically
"opt out" of each.  This behavior is in place for backwards
compatibility with prior versions of the qt4-* Portfiles.  The question
has been raised as to why those aren't the defaults, as they typically
are in other ports -- i.e., do the minimum unless the user wants
otherwise.  Making them the defaults would also cut down on install time
for many (most?) users (who don't care about example, demos, or
debugging; they just want Qt to work as release).  Unless someone can
convince me otherwise, I'm inclined to make them the defaults.  Thanks
for your thoughts! - MLD