MINOR: stats: support the "desc" output format modifier for info and stat

Now "show info" and "show stat" can parse "desc" as an output format
modifier that will be passed down the chain to add some descriptions
to the fields depending on the format in use. For now it is not
exploited.
diff --git a/include/types/stats.h b/include/types/stats.h
index d078b67..8817746 100644
--- a/include/types/stats.h
+++ b/include/types/stats.h
@@ -34,6 +34,7 @@
 #define STAT_SHNODE     0x00000200      /* conf: show node name */
 #define STAT_SHDESC     0x00000400      /* conf: show description */
 #define STAT_SHLGNDS    0x00000800      /* conf: show legends */
+#define STAT_SHOW_FDESC 0x00001000      /* show the field descriptions when possible */
 
 #define STAT_BOUND      0x00800000	/* bound statistics to selected proxies/types/services */
 #define STAT_STARTED    0x01000000	/* some output has occurred */