manpage fix to stop saying CacheIPv4DNS is on by default

Stop saying in the manual that clients cache ipv4 dns answers from exit
relays. We haven't used them since 0.2.6.3-alpha, and in ticket 24050
we stopped even caching them as of 0.3.2.6-alpha, but we forgot to say
so in the man page.

Fixes bug 26052; bugfix on 0.3.2.6-alpha.

changes/bug26052

+  o Minor bugfixes (documentation):
+    - Stop saying in the manual that clients cache ipv4 dns answers
+      from exit relays. We haven't used them since 0.2.6.3-alpha, and
+      in ticket 24050 we stopped even caching them as of 0.3.2.6-alpha,
+      but we forgot to say so in the man page. Fixes bug 26052; bugfix
+      on 0.3.2.6-alpha.

doc/tor.1.txt

@@ -1237,7 +1237,7 @@ The following options are useful only for clients (that is, if
         flag is not supported.
     **CacheIPv4DNS**;;
         Tells the client to remember IPv4 DNS answers we receive from exit
-        nodes via this connection. (On by default.)
+        nodes via this connection.
     **CacheIPv6DNS**;;
         Tells the client to remember IPv6 DNS answers we receive from exit
         nodes via this connection.