BUG: integrate: Fix some issues with banded Jacobians in the ode classes.

In the vode integrator class, add a wrapper of the user's Jacobian function
in the banded case that pads the Jacobian matrix to match the size required
by the F2PY-generated wrapper.

Fix the handling of a banded Jacobian in the complex_ode class.
MAINT: integrate: a bit of clean up in some test code.