MINOR: init: add -dW and "zero-warning" to reject configs with warnings

Since some systems switched to service managers which hide all warnings
by default, some users are not aware of some possibly important warnings
and get caught too late with errors that could have been detected earlier.

This patch adds a new global keyword, "zero-warning" and an equivalent
command-line option "-dW" to refuse to start in case any warning is
detected. It is recommended to use these with configurations that are
managed by humans in order to catch mistakes very early.
diff --git a/include/types/global.h b/include/types/global.h
index 718cfd8..407fbff 100644
--- a/include/types/global.h
+++ b/include/types/global.h
@@ -48,6 +48,7 @@
 #define	MODE_FOREGROUND	0x40
 #define	MODE_MWORKER	0x80    /* Master Worker */
 #define	MODE_MWORKER_WAIT	0x100    /* Master Worker wait mode */
+#define	MODE_ZERO_WARNING       0x200    /* warnings cause a failure */
 
 /* list of last checks to perform, depending on config options */
 #define LSTCHK_CAP_BIND	0x00000001	/* check that we can bind to any port */