Improve SALT SN+host photo-z fits

[RickKessler]

Original snlc_fit code did a course grid search (zPhot, color, stretch) to estimate initial parameters, but only for SN-only fits. With zPHOT prior from host, code set zPhot(guess) = zPHOT(host), and searches grid for x1 and c. Should estimate initial zPHOT regardless of whether or not there is host prior, particularly of zPHOTERR is large.

[RickKessler]

for now, the updated code is invoked with DEBUG_FLAG=1219.
For SN-only, zPHOT grid is searched over entire photo-z bound. For SN+host, zPHOT is searched over zPHOT +_ 2 sigma_{zPHOT}.
Another subtle change is to search grid in zPHOT/(1+zPHOT) instead of zPHOT; this allow a slightly smaller grid to save some CPU.
CPU increase is 20% with this new initial param search.