rate_estimation.c: parallelize posterior sum

- use OpenMP to auto-parallelize.  won't work on systems that don't use GCC
  or clang

gstlal-inspiral/python/Makefile.am

@@ -26,6 +26,6 @@ pkgpython_PYTHON = \
 pkgpyexec_LTLIBRARIES = _rate_estimation.la
 
 _rate_estimation_la_SOURCES = rate_estimation.c
-_rate_estimation_la_CPPFLAGS = $(AM_CPPFLAGS) $(PYTHON_CPPFLAGS) -DMODULE_NAME="\"gstlal._rate_estimation\""
+_rate_estimation_la_CPPFLAGS = $(AM_CPPFLAGS) $(PYTHON_CPPFLAGS) -DMODULE_NAME="\"gstlal._rate_estimation\"" -fopenmp
 _rate_estimation_la_CFLAGS = $(AM_CFLAGS) -DMODULE_NAME="\"gstlal._rate_estimation\""
-_rate_estimation_la_LDFLAGS = $(AM_LDFLAGS) $(PYTHON_LDFLAGS) -module -avoid-version
+_rate_estimation_la_LDFLAGS = $(AM_LDFLAGS) $(PYTHON_LDFLAGS) -module -avoid-version -fopenmp

gstlal-inspiral/python/rate_estimation.c

@@ -87,6 +87,7 @@ static double compute_log_posterior(const double *ln_f_over_b, int n, double Rf,
 		return atof("-inf");
 
 	ln_P = 0.;
+	#pragma omp parallel for reduction(+:ln_P)
 	for(i = 0; i < n; i++) {
 		/*
 		 * need to add log(Rf f / (Rb b) + 1) to sum.  if Rf f /