who,less: tweaked help text

function                                             old     new   delta
packed_usage                                       29176   29173      -3

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

coreutils/who.c

@@ -48,6 +48,7 @@
 //usage:#define who_full_usage "\n\n"
 //usage:       "Show who is logged on\n"
 //usage:     "\n	-a	Show all"
+//usage:     "\n	-a	Print column headers"
 
 #include "libbb.h"