[GRASS5] optional features defaulting to yes

[Hamish]

I notice that several optional features are defaulting to yes in the
./configure step, leading to confusion about the mandatory prereq's are.

http://grass.ibiblio.org/grass60/source/REQUIREMENTS.html

while for libpng, tcltk I can see that a default of "yes" is desirable,
should this be true for lesser used features? 

e.g.
  --with-postgres     support PostgreSQL functionality (default: yes)
  --with-fftw         support FFTW functionality (default: yes)


(mostly speaking of postgres here. why is it treated differently than
MySQL?)



Hamish