Merge of r4698: X-Forwarded-For conditionals.

Fixed compile-time conditionals used to detect if X-Forwarded-For support
is needed.

Note: compatibility shims were added during merge to avoid possible
breakage of 3rd party modules.  At least cache purge module was broken
by the original commit, as it used to rely on NGX_HTTP_PROXY define.

auto/modules

@@ -223,6 +223,7 @@ fi
 
 if [ $HTTP_REALIP = YES ]; then
     have=NGX_HTTP_REALIP . auto/have
+    have=NGX_HTTP_X_FORWARDED_FOR . auto/have
     HTTP_MODULES="$HTTP_MODULES $HTTP_REALIP_MODULE"
     HTTP_SRCS="$HTTP_SRCS $HTTP_REALIP_SRCS"
 fi
@@ -234,11 +235,13 @@ fi
 
 if [ $HTTP_GEO = YES ]; then
     have=NGX_HTTP_GEO . auto/have
+    have=NGX_HTTP_X_FORWARDED_FOR . auto/have
     HTTP_MODULES="$HTTP_MODULES $HTTP_GEO_MODULE"
     HTTP_SRCS="$HTTP_SRCS $HTTP_GEO_SRCS"
 fi
 
 if [ $HTTP_GEOIP = YES ]; then
+    have=NGX_HTTP_X_FORWARDED_FOR . auto/have
     HTTP_MODULES="$HTTP_MODULES $HTTP_GEOIP_MODULE"
     HTTP_SRCS="$HTTP_SRCS $HTTP_GEOIP_SRCS"
 fi
@@ -274,6 +277,7 @@ fi
 
 if [ $HTTP_PROXY = YES ]; then
     have=NGX_HTTP_PROXY . auto/have
+    have=NGX_HTTP_X_FORWARDED_FOR . auto/have
     #USE_MD5=YES
     HTTP_MODULES="$HTTP_MODULES $HTTP_PROXY_MODULE"
     HTTP_DEPS="$HTTP_DEPS $HTTP_PROXY_DEPS"

src/http/ngx_http_request.c

@@ -138,7 +138,7 @@ ngx_http_header_t  ngx_http_headers_in[] = {
     { ngx_string("Keep-Alive"), offsetof(ngx_http_headers_in_t, keep_alive),
                  ngx_http_process_header_line },
 
-#if (NGX_HTTP_PROXY || NGX_HTTP_REALIP || NGX_HTTP_GEO)
+#if (NGX_HTTP_X_FORWARDED_FOR)
     { ngx_string("X-Forwarded-For"),
                  offsetof(ngx_http_headers_in_t, x_forwarded_for),
                  ngx_http_process_header_line },

src/http/ngx_http_request.h

@@ -137,6 +137,13 @@
 #define NGX_HTTP_COPY_BUFFERED             0x04
 
 
+#if (NGX_HTTP_PROXY || NGX_HTTP_REALIP || NGX_HTTP_GEO)
+#ifndef NGX_HTTP_X_FORWARDED_FOR
+#define NGX_HTTP_X_FORWARDED_FOR           1
+#endif
+#endif
+
+
 typedef enum {
     NGX_HTTP_INITING_REQUEST_STATE = 0,
     NGX_HTTP_READING_REQUEST_STATE,
@@ -192,7 +199,7 @@ typedef struct {
 
     ngx_table_elt_t                  *keep_alive;
 
-#if (NGX_HTTP_PROXY || NGX_HTTP_REALIP || NGX_HTTP_GEO)
+#if (NGX_HTTP_X_FORWARDED_FOR)
     ngx_table_elt_t                  *x_forwarded_for;
 #endif
 

src/http/ngx_http_variables.c

@@ -134,7 +134,7 @@ static ngx_http_variable_t  ngx_http_core_variables[] = {
       offsetof(ngx_http_request_t, headers_in.via), 0, 0 },
 #endif
 
-#if (NGX_HTTP_PROXY || NGX_HTTP_REALIP)
+#if (NGX_HTTP_X_FORWARDED_FOR)
     { ngx_string("http_x_forwarded_for"), NULL, ngx_http_variable_header,
       offsetof(ngx_http_request_t, headers_in.x_forwarded_for), 0, 0 },
 #endif