Support for doing DNS at the proxy end. I've invented a new type of

SockAddr, which just contains an unresolved hostname and is created
by a stub function in *net.c. It's an error to pass this to most of
the real-meat functions in *net.c; these fake addresses should have
been dealt with by the time they get down that far. proxy.c now
contains name_lookup(), a wrapper on sk_namelookup() which decides
whether or not to do real DNS, and the individual proxy
implementations each deal sensibly with being handed an unresolved
address and avoid ever passing one down to *net.c.

[originally from svn r2353]

putty.h

@@ -214,6 +214,7 @@ struct config_tag {
     int tcp_nodelay;
     /* Proxy options */
     char proxy_exclude_list[512];
+    enum { PROXYDNS_NO, PROXYDNS_AUTO, PROXYDNS_YES } proxy_dns;
     int even_proxy_localhost;
     enum { PROXY_NONE, PROXY_HTTP, PROXY_SOCKS, PROXY_TELNET } proxy_type;
     char proxy_host[512];