graphics/blender: Make use of OpenAL configurable

[Christian Walther]

Hi,

I have a suggestion for the graphics/blender port, because blenders
Makefile states that OpenAL can be disabled:
# To build without openAL, uncomment the following line, or set it as
# an environment variable, or put it uncommented in user-def.mk:
# export NAN_NO_OPENAL=true

Not every blender user requires OpenAL I guess, so it would be great
to have OpenAL as an option selectable during "make config", or having
NAN_NO_OPENAL exported so that it can be defined in /etc/make.conf.
This would reduce the binary size, probably even the amount of
installed ports, and exploit one major benefit of the ports system.

Maybe it would even make sense to integrate BLENDERGAMEENGINE and
BLENDERPLAYER user selectable. Personally, I don't think that I'll
need any of the two.

Regards
Christian Walther