Don't include background.h if it's not needed.

If needed, add explanation.

src/boxes.c

@@ -44,7 +44,7 @@
 #include "main.h"		/* For the confirm_* variables */
 #include "tree.h"
 #include "layout.h"		/* for get_nth_panel_name proto */
-#include "background.h"
+#include "background.h"		/* task_list */
 
 #ifdef HAVE_CHARSET
 #include "charsets.h"

src/file.c

@@ -65,7 +65,7 @@
 #include "layout.h"
 #include "widget.h"
 #include "wtools.h"
-#include "background.h"		/* tell_parent() */
+#include "background.h"		/* we_are_background */
 
 /* Needed for current_panel, other_panel and WTree */
 #include "dir.h"

src/filegui.c

@@ -60,7 +60,6 @@
 #include "setup.h"		/* verbose */
 #include "dialog.h"		/* do_refresh() */
 #include "color.h"		/* dialog_colors */
-#include "background.h"		/* message */
 #include "widget.h"		/* WLabel */
 #define WANT_WIDGETS
 #include "main.h"		/* the_hint */

src/main.c

@@ -63,7 +63,6 @@
 #include "panelize.h"
 #include "learn.h"		/* learn_keys() */
 #include "listmode.h"
-#include "background.h"
 #include "execute.h"
 #include "ext.h"		/* For flush_extension_file() */