MEDIUM: initcall: use initcalls for a few initialization functions

signal_init(), init_log(), init_stream(), and init_task() all used to
only preset some values and lists. This needs to be done very early to
provide a reliable interface to all other users. The calls used to be
explicit in haproxy.c:init(). Now they're placed in initcalls at the
STG_PREPARE stage. The functions are not exported anymore.
diff --git a/src/log.c b/src/log.c
index 77d58e2..3093cce 100644
--- a/src/log.c
+++ b/src/log.c
@@ -1581,9 +1581,8 @@
 		} while(0)
 
 
-/* Initializes some log data.
- */
-void init_log()
+/* Initializes some log data at boot */
+static void init_log()
 {
 	char *tmp;
 	int i;
@@ -1656,6 +1655,8 @@
 	FD_SET(0x7f, http_encode_map);
 }
 
+INITCALL0(STG_PREPARE, init_log);
+
 static int init_log_buffers_per_thread()
 {
 	return init_log_buffers();