MEDIUM: New cli option -Ds for systemd compatibility

This patch adds a new option "-Ds" which is exactly like "-D", but instead of
forking n times to get n jobs running and then exiting, prefers to wait for all the
children it just created. With this done, haproxy becomes more systemd-compliant,
without changing anything for other systems.

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
diff --git a/include/types/global.h b/include/types/global.h
index 133a98d..730cc64 100644
--- a/include/types/global.h
+++ b/include/types/global.h
@@ -42,6 +42,7 @@
 #define	MODE_VERBOSE	0x10
 #define	MODE_STARTING	0x20
 #define	MODE_FOREGROUND	0x40
+#define	MODE_SYSTEMD	0x80
 
 /* list of last checks to perform, depending on config options */
 #define LSTCHK_CAP_BIND	0x00000001	/* check that we can bind to any port */