Lyman alpha contribute to photoelectric heating

1. Lyman alpha is attenuated by H2O, OH, and dust
Correted a bug in neighbor finding

1. That's related to the tolerance used to decide whether two rectangles have a
   common side.  The tolerance was set to a fixed number, and it was too large
   for small cells (especially when a few levels refinement have been
   conducted).  Now I set it to be a fraction of the smallest dimension of the
   two rectangles being considered (and must also be smaller than a fraction
   (0.01) of the smallest size scale we are going to consider).
2. Set a size limit for refinement.
3. Adjusted (slightly) the logic for whether do a refinment.