http-proxy: move proxy code to http_proxy.c

The new http_proxy.* files now host HTTP proxy specific code (500+ lines
moved out from http.c), and as a consequence there is a macro introduced
for the Curl_proxyCONNECT() function so that code can use it without
actually supporting proxy (or HTTP) in builds.

lib/imap.c

@@ -85,6 +85,7 @@
 #include "url.h"
 #include "rawstr.h"
 #include "strtoofft.h"
+#include "http_proxy.h"
 
 #define _MPRINTF_REPLACE /* use our functions only */
 #include <curl/mprintf.h>
@@ -718,7 +719,6 @@ static CURLcode imap_connect(struct connectdata *conn,
   pp->endofresp = imap_endofresp;
   pp->conn = conn;
 
-#if !defined(CURL_DISABLE_HTTP) && !defined(CURL_DISABLE_PROXY)
   if(conn->bits.tunnel_proxy && conn->bits.httpproxy) {
     /* for IMAP over HTTP proxy */
     struct HTTP http_proxy;
@@ -745,7 +745,6 @@ static CURLcode imap_connect(struct connectdata *conn,
     if(CURLE_OK != result)
       return result;
   }
-#endif /* !CURL_DISABLE_HTTP && !CURL_DISABLE_PROXY */
 
   if((conn->handler->protocol & CURLPROTO_IMAPS) &&
      data->state.used_interface != Curl_if_multi) {