Merge branch 'clear_bh_flag' into 'master'

Clear bh drift flag

See merge request !1073

src/cell.c

@@ -2427,6 +2427,7 @@ void cell_clean(struct cell *c) {
 void cell_clear_drift_flags(struct cell *c, void *data) {
   cell_clear_flag(c, cell_flag_do_hydro_drift | cell_flag_do_hydro_sub_drift |
                          cell_flag_do_grav_drift | cell_flag_do_grav_sub_drift |
+                         cell_flag_do_bh_drift | cell_flag_do_bh_sub_drift |
                          cell_flag_do_stars_drift |
                          cell_flag_do_stars_sub_drift);
 }