Add use of proxy to startup messages

[Ageless]

At this moment any client that starts up shows about everything that the client can do and has set as options and settings. I'm requesting that a notification that a proxy is in use is added to this.

So that it shows something like this:
Starting BOINC client version x.x.x for platform
log flags: task, file_xfer, sched_ops
Libraries: libcurl/7.18.0 OpenSSL/0.9.8e zlib/1.2.3
Data directory: C:\Program Files\BOINC
Processor: processor detection
Processor features: fpu tsc pae nx sse sse2 mmx
OS: Operating system
Memory: x.00 GB physical, x.xx GB virtual
Disk: xx GB total, xx GB free
Local time is UTC +x hours
No coprocessors
Proxy used: None/HTTP/Socks

Where it shows None when none is in use and either HTTP or Socks depending on which one is in use. It helps us when diagnosing people's problems and they post their messages.

[Nicolas]

+1

[Pepo]

Replying to Ageless:

Proxy used: None/HTTP/Socks

The notification might then also appear each time the proxy setting is changed on the fly. (I'm aware that the message will possibly disappear among other messages.)

[davea]

(In [15716]) - client: show proxy info in messages at startup and when changed

fixes #704

• web: fix the am_set_info.php RPC

(most args are optional, not mandatory)

[Pepo]

Replying to davea:

(In [15716]) - client: show proxy info in messages at startup and when changed

fixes #704

Switching off the proxy (or not using it at the beginning) is not reported.

Why not report all states, something like

void CLIENT_STATE::show_proxy_info() {
    if (proxy_info.use_http_proxy) {
        msg_printf(NULL, MSG_INFO, "Using HTTP proxy %s:%d",
            proxy_info.http_server_name, proxy_info.http_server_port
        );
    }
    else if (proxy_info.use_socks_proxy) {
        msg_printf(NULL, MSG_INFO, "Using SOCKS proxy %s:%d",
             proxy_info.socks_server_name, proxy_info.socks_server_port
        );
    }
    else {
        msg_printf(NULL, MSG_INFO, "Not using a proxy");
    }
}

[davea]

(In [15717]) - client: show message if no proxy

fixes #704