MINOR: debug/cli: add some debugging commands for developers

When haproxy is built with DEBUG_DEV, the following commands are added
to the CLI :

  debug dev close <fd>        : close this file descriptor
  debug dev delay [ms]        : sleep this long
  debug dev exec  [cmd] ...   : show this command's output
  debug dev exit  [code]      : immediately exit the process
  debug dev hex   <addr> [len]: dump a memory area
  debug dev log   [msg] ...   : send this msg to global logs
  debug dev loop  [ms]        : loop this long
  debug dev panic             : immediately trigger a panic
  debug dev tkill [thr] [sig] : send signal to thread

These are essentially aimed at helping developers trigger certain
conditions and are expected to be complemented over time.
diff --git a/Makefile b/Makefile
index ddf29f0..3248819 100644
--- a/Makefile
+++ b/Makefile
@@ -209,8 +209,8 @@
 #### Debug settings
 # You can enable debugging on specific code parts by setting DEBUG=-DDEBUG_xxx.
 # Currently defined DEBUG macros include DEBUG_FULL, DEBUG_MEMORY, DEBUG_FSM,
-# DEBUG_HASH, DEBUG_AUTH, DEBUG_SPOE, DEBUG_UAF and DEBUG_THREAD. Please check
-# sources for exact meaning or do not use at all.
+# DEBUG_HASH, DEBUG_AUTH, DEBUG_SPOE, DEBUG_UAF and DEBUG_THREAD, DEBUG_STRICT,
+# DEBUG_DEV. Please check sources for exact meaning or do not use at all.
 DEBUG =
 
 #### Trace options