Modifications to make the exporter consistent with OSG examples

Hello Cedric, 

I have encountered problems while trying to use the exporter with osgAnimation code based on the OSG examples. It seems that there are some inconsistencies, namely the naming of the quaternion stacked transform ("quaternion" vs "rotate" in the examples) and the way the skeleton pose is exported. OSG is using translation/quaternion/scale as the rest pose from which the animations are referenced, however your exporter exports these as identity transform and exports a matrix called "bindmatrix" instead - which is ignored by the OSG examples. 

I have changed the code to match with the OSG example code, but probably you had your own reason why did you do things in the way you did, that's why I have it a branch for the time being. However, it would be good to fix this, because it will trip up anyone who follows the examples and then tries to use your exporter to actually produce some animated models.

I have also fixed one version check (the FILENAME vs FILE_NAME issue) that was tested  incorrectly and was crashing for me inside Blender while debugging (b'foo' creates a byte array and this was being compared to a string => crash due to incompatible types). 

Regards,

Jan