update master according to recent bugfix in develop (see description below)

Fixed small bug in the computation of "low_prob_rec" (was correct in LyaPhotonsFromGas but the normalisation was wrong in PhotonsFromStars.f90). Also fixed the binary searches (in both LyaPhotonsFromGas and PhotonsFromStars) where iup was initialised to n instead of n+1.

These bugs had generally no impact, except for objects with very few sources (e.g. a few star particles or a few cells).