include config.h in all sources

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

scripts/check_config_h.rb

@@ -0,0 +1,47 @@
+#!/usr/bin/env ruby
+#
+# This script verifies that every source includes config.h first.
+# This is very important for consistent Large File Support.
+#
+
+def check_file(file)
+    first = true
+    file.each_line do |line|
+        if line =~ /^\#include\s+(\S+)/ then
+            if $1 == '"config.h"'
+                unless first
+                    puts "#{file.path}: config.h included too late"
+                end
+            else
+                if first
+                    puts "#{file.path}: config.h missing"
+                end
+            end
+            first = false
+        end
+    end
+end
+
+def check_path(path)
+    File.open(path) do |file|
+        check_file(file)
+    end
+end
+
+if ARGV.empty?
+    Dir["src/*.c"].each do |path|
+        check_path(path)
+    end
+
+    Dir["src/*/*.c"].each do |path|
+        check_path(path)
+    end
+
+    Dir["test/*.c"].each do |path|
+        check_path(path)
+    end
+else
+    ARGV.each do |path|
+        check_path(path)
+    end
+end