cygwin build: --enable-png or jpeg

Hi

I'm trying to build PLPlot to output graphs and contour
plots as PNG and/or JPEG images, on cygwin and MinGW.
Trying on cygwin (latest), I can't seem to get the
build options for using the GD library correct. I think
the ./configure documentation might be wrong?

john@cruncher2 ~/plplot-5.2.1.rc2.5.3.0
$ ./configure --help=short

...

john@cruncher2 ~/plplot-5.2.1.rc2.5.3.0
$ ./configure --enable-png --enable-cxx
configure: error: invalid feature name: png

john@cruncher2 ~/plplot-5.2.1.rc2.5.3.0
$ ./configure --enable-jpeg --enable-cxx
configure: error: invalid feature name: jpeg

Cheers

JP