MINOR: config: mark global.debug as deprecated
This directive has never made any sense and has already caused trouble
by forcing the process to stay in foreground during the boot process.
Let's emit a warning mentioning it's deprecated and will be removed in
2.3.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index c20311d..6cb641e 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -2159,7 +2159,7 @@
3.3. Debugging
--------------
-debug
+debug (deprecated)
Enables debug mode which dumps to stdout all exchanges, and disables forking
into background. It is the equivalent of the command-line argument "-d". It
should never be used in a production configuration since it may prevent full