Modules compatibility: compatibility with NGX_HAVE_FILE_AIO.

With this change it is now possible to load modules compiled without
the "--with-file-aio" configure option into nginx binary compiled with it,
and vice versa, assuming both use the "--with-compat" option.

src/core/ngx_buf.h

diff --git a/src/core/ngx_buf.h b/src/core/ngx_buf.h
index 224807c..12781a7 100644
--- a/src/core/ngx_buf.h
+++ b/src/core/ngx_buf.h
@@ -72,10 +72,8 @@
 
 typedef ngx_int_t (*ngx_output_chain_filter_pt)(void *ctx, ngx_chain_t *in);
 
-#if (NGX_HAVE_FILE_AIO)
 typedef void (*ngx_output_chain_aio_pt)(ngx_output_chain_ctx_t *ctx,
     ngx_file_t *file);
-#endif
 
 struct ngx_output_chain_ctx_s {
     ngx_buf_t                   *buf;
@@ -90,9 +88,9 @@
     unsigned                     need_in_temp:1;
     unsigned                     aio:1;
 
-#if (NGX_HAVE_FILE_AIO)
+#if (NGX_HAVE_FILE_AIO || NGX_COMPAT)
     ngx_output_chain_aio_pt      aio_handler;
-#if (NGX_HAVE_AIO_SENDFILE)
+#if (NGX_HAVE_AIO_SENDFILE || NGX_COMPAT)
     ssize_t                    (*aio_preload)(ngx_buf_t *file);
 #endif
 #endif

src/core/ngx_connection.h

diff --git a/src/core/ngx_connection.h b/src/core/ngx_connection.h
index b527954..a49c5a6 100644
--- a/src/core/ngx_connection.h
+++ b/src/core/ngx_connection.h
@@ -182,7 +182,7 @@
 
     unsigned            need_last_buf:1;
 
-#if (NGX_HAVE_AIO_SENDFILE)
+#if (NGX_HAVE_AIO_SENDFILE || NGX_COMPAT)
     unsigned            busy_count:2;
 #endif
 

src/core/ngx_file.h

diff --git a/src/core/ngx_file.h b/src/core/ngx_file.h
index cff74cb..320adc2 100644
--- a/src/core/ngx_file.h
+++ b/src/core/ngx_file.h
@@ -30,7 +30,7 @@
     ngx_thread_task_t         *thread_task;
 #endif
 
-#if (NGX_HAVE_FILE_AIO)
+#if (NGX_HAVE_FILE_AIO || NGX_COMPAT)
     ngx_event_aio_t           *aio;
 #endif
 

src/core/ngx_module.h

diff --git a/src/core/ngx_module.h b/src/core/ngx_module.h
index 626481d..4d0db44 100644
--- a/src/core/ngx_module.h
+++ b/src/core/ngx_module.h
@@ -35,13 +35,13 @@
 #define NGX_MODULE_SIGNATURE_2   "0"
 #endif
 
-#if (NGX_HAVE_FILE_AIO)
+#if (NGX_HAVE_FILE_AIO || NGX_COMPAT)
 #define NGX_MODULE_SIGNATURE_3   "1"
 #else
 #define NGX_MODULE_SIGNATURE_3   "0"
 #endif
 
-#if (NGX_HAVE_AIO_SENDFILE)
+#if (NGX_HAVE_AIO_SENDFILE || NGX_COMPAT)
 #define NGX_MODULE_SIGNATURE_4   "1"
 #else
 #define NGX_MODULE_SIGNATURE_4   "0"

src/event/ngx_event.h

diff --git a/src/event/ngx_event.h b/src/event/ngx_event.h
index f0b75af..053bd16 100644
--- a/src/event/ngx_event.h
+++ b/src/event/ngx_event.h
@@ -152,7 +152,7 @@
     ngx_event_handler_pt       handler;
     ngx_file_t                *file;
 
-#if (NGX_HAVE_AIO_SENDFILE)
+#if (NGX_HAVE_AIO_SENDFILE || NGX_COMPAT)
     ssize_t                  (*preload_handler)(ngx_buf_t *file);
 #endif
 

src/http/ngx_http_core_module.c

diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index 2daea10..9da5d10 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -3760,10 +3760,8 @@
     ngx_conf_merge_value(conf->sendfile, prev->sendfile, 0);
     ngx_conf_merge_size_value(conf->sendfile_max_chunk,
                               prev->sendfile_max_chunk, 0);
-#if (NGX_HAVE_FILE_AIO || NGX_THREADS)
     ngx_conf_merge_value(conf->aio, prev->aio, NGX_HTTP_AIO_OFF);
     ngx_conf_merge_value(conf->aio_write, prev->aio_write, 0);
-#endif
 #if (NGX_THREADS)
     ngx_conf_merge_ptr_value(conf->thread_pool, prev->thread_pool, NULL);
     ngx_conf_merge_ptr_value(conf->thread_pool_value, prev->thread_pool_value,