Complain when bwa mem is given too many filenames

Reads in extra .fq filenames beyond "bwa mem index one.fq two.fq"
will not be aligned, so complain about such invalid usage instead.

fastmap.c

@@ -54,7 +54,7 @@ int main_mem(int argc, char *argv[])
 		else return 1;
 	}
 	if (opt->n_threads < 1) opt->n_threads = 1;
-	if (optind + 1 >= argc) {
+	if (optind + 1 >= argc || optind + 3 < argc) {
 		fprintf(stderr, "\n");
 		fprintf(stderr, "Usage: bwa mem [options] <idxbase> <in1.fq> [in2.fq]\n\n");
 		fprintf(stderr, "Algorithm options:\n\n");