[FGS] fgs, gdal, and doxygen

[shawn barnes]

Frank is there a way to build gdal without doxygen.  i've added doxygen
to the fgs-dev that i've been testing on, just for gdal but i think i
would, prefer to not need doxygen in fgs-dev.

The reason i added doxygen into fgs-dev is because in installing doxygen
the system also installed all of it's dependencies (freetype, jpeg, png,
etc. etc....) and i've been trying to keep the base system very 'clean'
so fgs-dev doesn't use anything outside of it's env to build against.

shawn