dpkg-deb: Document --debug in --help output

debian/changelog

@@ -2,6 +2,7 @@ dpkg (1.17.0) UNRELEASED; urgency=low
 
   * Switch update-alternatives back to a fatal error on out of range priority
     on --install.
+  * Document dpkg-deb --debug in --help output.
 
  -- Guillem Jover <guillem@debian.org>  Fri, 03 Aug 2012 13:21:00 +0200
 

dpkg-deb/main.c

@@ -101,7 +101,7 @@ usage(const struct cmdinfo *cip, const char *value)
 "Options:\n"
 "  --showformat=<format>            Use alternative format for --show.\n"
 "  -v, --verbose                    Enable verbose output.\n"
-"  -D                               Enable debugging output.\n"
+"  -D, --debug                      Enable debugging output.\n"
 "  --old, --new                     Select archive format.\n"
 "  --nocheck                        Suppress control file check (build bad\n"
 "                                     packages).\n"