better way to handle required rebuild on library bump

[Eitan Adler]

With due respect to the creativity of the OP, the whole conversation is
basically moot since in almost all cases a library major version change
requires a change to the LIB_DEPENDS line in the port anyway, so a
PORTREVISION bump is a very tiny bit of additional work.

Ah, I did not realize this. As you said my point is moot anyway.