fuse three OpenMP parallel regions into one
fuse three OpenMP parallel regions into one

this matters for large thread counts and when OpenMP runtime overhead is
high.

snelliott/aquarius,snelliott/aquarius,jeffhammond/aquarius,jeffhammond/aquarius,samblau/aquarius,devinamatthews/aquarius,samblau/aquarius,snelliott/aquarius,samblau/aquarius,devinamatthews/aquarius,jeffhammond/aquarius,devinamatthews/aquarius,devinamatthews/aquarius,snelliott/aquarius,jeffhammond/aquarius,samblau/aquarius