Added GIL release in TaskBatch::execute() bindings.
Added GIL release in TaskBatch::execute() bindings.

This is necessary to allow Executable::execute() implementations to use threads if they wish, in case those threads need to enter Python.

hradec/gaffer,GafferHQ/gaffer,goddardl/gaffer,ivanimanishi/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,ivanimanishi/gaffer,chippey/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,appleseedhq/gaffer,goddardl/gaffer,boberfly/gaffer,appleseedhq/gaffer,andrewkaufman/gaffer,appleseedhq/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,hradec/gaffer,cedriclaunay/gaffer,lucienfostier/gaffer,chippey/gaffer,boberfly/gaffer,GafferHQ/gaffer,cedriclaunay/gaffer,ivanimanishi/gaffer,boberfly/gaffer,andrewkaufman/gaffer,boberfly/gaffer,johnhaddon/gaffer,hradec/gaffer,ImageEngine/gaffer,goddardl/gaffer,ivanimanishi/gaffer,appleseedhq/gaffer,hradec/gaffer,johnhaddon/gaffer,lucienfostier/gaffer,chippey/gaffer,cedriclaunay/gaffer,lucienfostier/gaffer,hradec/gaffer,chippey/gaffer,GafferHQ/gaffer,lucienfostier/gaffer,cedriclaunay/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,goddardl/gaffer,GafferHQ/gaffer,ImageEngine/gaffer