REORG: include: move task.h to haproxy/task{,-t}.h

The TASK_IS_TASKLET() macro was moved to the proto file instead of the
type one. The proto part was a bit reordered to remove a number of ugly
forward declaration of static inline functions. About a tens of C and H
files had their dependency dropped since they were not using anything
from task.h.
diff --git a/src/proxy.c b/src/proxy.c
index 5d42217..71ad054 100644
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -24,6 +24,7 @@
 #include <haproxy/listener.h>
 #include <haproxy/obj_type-t.h>
 #include <haproxy/pool.h>
+#include <haproxy/task.h>
 #include <haproxy/time.h>
 
 #include <import/eb32tree.h>
@@ -47,7 +48,6 @@
 #include <proto/signal.h>
 #include <proto/stream.h>
 #include <proto/stream_interface.h>
-#include <proto/task.h>
 
 
 int listeners;	/* # of proxy listeners, set by cfgparse */