plug-ins: fix build warnings.

Fixes several missing declaration warnings because in fact of missing include,
such as:

> warning: no previous declaration for ‘console_editor_new’ [-Wmissing-declarations]

Fixes 2 old-style definitions:

> warning: old-style function definition [-Wold-style-definition]

plug-ins/script-fu/console/script-fu-console-editor.c

@@ -19,6 +19,8 @@
 
 #include <gtk/gtk.h>
 
+#include "script-fu-console-editor.h"
+
 
 /* ConsoleEditor
 
@@ -40,7 +42,7 @@
  */
 
 GtkWidget *
-console_editor_new ()
+console_editor_new (void)
 {
   return gtk_entry_new ();
 }

plug-ins/script-fu/console/script-fu-console-total.c

@@ -35,7 +35,7 @@
 
 
 GtkTextBuffer *
-console_total_history_new ()
+console_total_history_new (void)
 {
   return gtk_text_buffer_new (NULL);
 }