Add cleanup to trainfromFiles and move RANDOM_segment_t declaration

contrib/randomDictBuilder/random.c

@@ -47,6 +47,15 @@ static size_t RANDOM_sum(const size_t *samplesSizes, unsigned nbSamples) {
 }
 
 
+/**
+ * A segment is an inclusive range in the source.
+ */
+typedef struct {
+  U32 begin;
+  U32 end;
+} RANDOM_segment_t;
+
+
 /**
  * Selects a random segment from totalSamplesSize - k + 1 possible segments
  */