Dual licensing syntax

[Joshua Root]

There are two ways a port can have multiple licenses. There may be a set
of licenses all of which apply (e.g. OpenSSL), or a choice of one
license from the set may be offered (e.g. Perl). There could also be a
combination of these.

We don't currently have a syntax for the case where there's a choice.
I'd suggest separating them with a pipe; so for example the perl5.12
portfile would say:

license		Artistic|GPL

and a perl module incorporating some BSD-licensed files might say:

license		Artistic|GPL BSD

Any objections or better ideas?

- Josh