add cal3d contribution to scons

[shaegler]

two minor additions are necessary to enable Cal3D contribution in scons, here is the diff...

Index: SConstruct

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RCS file: /cvsroot/opensg/OpenSG/SConstruct,v

retrieving revision 1.54

diff -r1.54 SConstruct

517a518

opts.Add(BoolOption?('contrib_cal3d', 'enable Cal3D character animation library wrapper core', 0))

Index: Source/Contrib?/SConscript

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RCS file: /cvsroot/opensg/OpenSG/Source/Contrib/SConscript,v

retrieving revision 1.8

diff -r1.8 SConscript

34a35,37

if _po.getOption('contrib_cal3d'):

ContribDirs?.append(Dir('Cal3D'))