r876: skip DP if taking too much RAM (#259)

minimap.h

@@ -139,6 +139,7 @@ typedef struct {
 	int32_t mid_occ;     // ignore seeds with occurrences above this threshold
 	int32_t max_occ;
 	int mini_batch_size; // size of a batch of query bases to process in parallel
+	int64_t max_sw_mat;
 
 	const char *split_prefix;
 } mm_mapopt_t;