Merge branch 'master' into Wconversion
Fixed warnings from -Wconversion (and -Wno-sign-conversion).
Fixed up network-mpi.c with casts.

God help us if an implementation chooses to do something other than
truncate when downcasting.
Merge branch 'Wconversion'

Cleaned up the warnings from the -Wconversion flag (minus the warnings
from sign conversion).  Everything seems kosher.