Module API for Forking

* create module API for forking child processes.
* refactor duplicate code around creating and tracking forks by AOF and RDB.
* child processes listen to SIGUSR1 and dies exitFromChild in order to
  eliminate a valgrind warning of unhandled signal.
* note that BGSAVE error reply has changed.

valgrind error is:
  Process terminating with default action of signal 10 (SIGUSR1)

1 files changed, 2 insertions, 0 deletions

diff --git a/src/childinfo.c b/src/childinfo.c
index 719025e8c..fa0600552 100644
--- a/src/childinfo.c
+++ b/src/childinfo.c
@@ -80,6 +80,8 @@ void receiveChildInfo(void) {
             server.stat_rdb_cow_bytes = server.child_info_data.cow_size;
         } else if (server.child_info_data.process_type == CHILD_INFO_TYPE_AOF) {
             server.stat_aof_cow_bytes = server.child_info_data.cow_size;
+        } else if (server.child_info_data.process_type == CHILD_INFO_TYPE_MODULE) {
+            server.stat_module_cow_bytes = server.child_info_data.cow_size;
         }
     }
 }