update control spec to reflect our new SETCONF behavior

svn:r5038

doc/control-spec.txt

@@ -110,9 +110,9 @@ $Id$
 
   Tor behaves as though it had just read each of the key-value pairs
   from its configuration file.  Keywords with no corresponding values have
-  their configuration values reset to their defaults.  SETCONF is
-  all-or-nothing: if there is an error in any of the configuration settings,
-  Tor sets none of them.
+  their configuration values reset to 0 or "" (use RESETCONF if you want
+  to set it back to its default).  SETCONF is all-or-nothing: if there
+  is an error in any of the configuration settings, Tor sets none of them.
 
   Tor responds with a "250 configuration values set" reply on success.
   Tor responds with a "513 syntax error in configuration values" reply on