Add options to a port.

[Dave Hardman]

	Following a recent ports updating gnucash crashes with a
segmentation fault. I've been advised to enable debugging to track down
the problem. This is done
by enabling the option --enable-debug to the config. My problem is that
I don't know how to do this within the ports system. It looks as if this
is done by adding an option to the makefile. I'm uncertain of what
changes need to be made. 

I would be grateful for advice on this. 


Thanks

Dave