Add flush_my_map_info_list() and fix a bug in the Mac load_map_info_list().

(If you fclose(3) rather than pclose(3) a FILE* you got from popen(3),
future popen(3)s fail obscurely, at least on Mac OS.)

(cherry picked from commit 2bf76e143da933184d1392fb9bea3a3896c37e76)

Change-Id: I5578fe06753061b0dbc5ee951ebf31eb2bab0389
diff --git a/libcorkscrew/test.cpp b/libcorkscrew/test.cpp
index 6f7be3b..22dfa7d 100644
--- a/libcorkscrew/test.cpp
+++ b/libcorkscrew/test.cpp
@@ -66,6 +66,11 @@
 }
 
 int main() {
+  flush_my_map_info_list();
   f();
+
+  flush_my_map_info_list();
+  f();
+
   return 0;
 }