To enable it you will need to download OpenEXR and install it.
For the Makefiles you will need to set WITH_OPENEXR=true
and set NAN_OPENEXR to point to where OpenEXR is installed.
For scons you'll need to remove config.opts to get the new options
so you can enable OpenEXR, I was not able to get blender to link
with scons so the scons stuff may need to be tweaked a little but
I think it should work.
For other platform managers The OpenEXR stuff is similar to QUICKTIME
you need to define WITH_OPENEXR and setup the library stuff and
as you'll notice in this commit there are two extra files.
Kent