Add $\pm$ add field functions to subdomain header
Teach domains about plus and minus fields
Simplify subdomain face comparison functions
Cast bfam_locidx_t to intmax_t for printing

This just makes sure that the output is independent of the size of
integer used for bfam_locidx_t.  Also use snprintf out of paranoia.
Init subdomain send and recv funcs to NULL
Fix $\pm$ ids for the glue grid

We have to use a 1-based indexing because there is no a -0 for integers.
Initialize and free $\pm$ fields in the subdomain
Add $\pm$ id fields to DG quad glue
TEMP COMMIT!!!!