Second-stage refinement makes accuracy worse, not better

Using 333437be from the two-away branch, do the following:

• Insert a 1/0 in test/test_layer_pot_identity.py to avoid running for more than one resolution.

• Run

  PYOPENCL_TEST=port python test_layer_pot_identity.py  'test_identity_convergence(cl._csc, WobblyCircleGreenTest())'`

• Observe very poor accuracy: (that last number is the error)

  (3, 'wobbly-circle', 2000, 'green') 0.038146725565187

• Disable second-stage refinement by changing line 583 in pytential/qbx/refinement.py from

  while must_refine:

  to

  while 0 and must_refine:

• Re-run the above test and observe a much-improved error:

  (3, 'wobbly-circle', 2000, 'green') 2.668441871633514e-07

I don't believe this issue is connected to two-away, FWIW--that's just the branch where the test case lives. If you set fmm_order = False in WobblyCircleGreenTest, the above observations still hold.

@mattwala, any idea what might be going on here?