mxqsub: Implement --tmpdir argument without units

The usage string of mxqsub says, that any size can be given without
units, in which case Mebibytes is assumed.

This doesn't currently work for --tmpdir, because the function
mx_strtobytes which is used to convert the string, doesn't accept
numbers without units.

Try mx_strtou64() first to process numerical argments without a unit.
Because tmpdir size is stored in Gibibytes and not Mebibytes internally,
the value needs to be divided by 1024.

mxqsub.c

@@ -989,7 +989,10 @@ int main(int argc, char *argv[])
                 break;
 
             case 7:
-                {
+                u_int64_t  arg_tmpdir_mb;
+                if (mx_strtou64(optctl.optarg, &arg_tmpdir_mb) == 0) {
+                    arg_tmpdir = (arg_tmpdir_mb+1024-1)/1024;
+                } else {
                     unsigned long long int bytes;
                     if(mx_strtobytes(optctl.optarg, &bytes) < 0) {
                         mx_log_crit("--tmpdir '%s': %m", optctl.optarg);