One initial issue that you must consider if you wish to export
blend shapes is that if you attempt to query the original mesh
shape which has blend shapes applied, you will end up accesing
the deformed version rather than the base version.
To counter this problem, it is worth disabling all Blend Shape
deformers before you attempt to access the base shape.
All blend shape deformers in maya have an envelope
(en) attribute. This attribute can be set to 0 to disable
the actual effect. Therefore, before we export, we can disable
all of the blend shape deformers, and then re-enable them after
exporting the data.