alpha proposal: port options

[Gabor Tjong A Hung]

Hi there,
Could you also include a radio-like option in addition to the checkbox-like
options (
http://www.freebsd.org/doc/en_US.ISO8859-1/books/porters-handbook/makefile-options.html#AEN2476
)

This is useful for ports like eclipse where you need to specify either gecko
or firefox or mozilla etc.
or texmaker where you would preferably be able to chose acroread, xpdf etc.