Squash some GCC warnings about unsigned/signed comparisons

error.h

@@ -18,6 +18,7 @@ extern int myrank;
   ({                                                                     \
     printf("[%04i] %s %s: " s "\n", myrank, clocks_get_timesincestart(), \
            __FUNCTION__, ##__VA_ARGS__);                                 \
+    fflush(stdout);                                                      \
   })
 
 /* Print MPI error string. */

mpiuse.c

@@ -254,6 +254,6 @@ int mpiuse_nr_ranks(void) { return mpiuse_max_rank + 1; }
  */
 struct mpiuse_log_entry *mpiuse_get_log(int ind) {
 
-  if (ind < mpiuse_log_count && ind >= 0) return &mpiuse_log[ind];
+  if ((size_t)ind < mpiuse_log_count && ind >= 0) return &mpiuse_log[ind];
   return NULL;
 }

swiftmpistepsim.c

@@ -378,7 +378,7 @@ static void pick_logs(void) {
       nlogs, sizeof(struct mpiuse_log_entry *));
   nr_recvs = 0;
 
-  for (int k = 0; k < nlogs; k++) {
+  for (size_t k = 0; k < nlogs; k++) {
     struct mpiuse_log_entry *log = mpiuse_get_log(k);
     if (log->rank == myrank && log->activation) {
       if (log->type == task_type_send || log->type == task_type_recv) {