in-Portfile variant removal (not default)?

[Michael Dickens]

Thanks for the responses.  I think what I'll do is just not allow the +debug variant by itself, since Qt won't build just a framework debug version -- it either errors out or upgrades to +combined.  That makes the Portfiles for 4.6.3 and 4.7.0b2 (and, future ones, since this behavior won't change) consistent, which is also nice.  Now, the question is: I want the Portfile to generate an error if just +debug is selected.  How do I do that in a robust manner (e.g., after a "ui_msg" about why it's erroring out)? - MLD