move foreign function interface to its own module

* libguile/foreign.h:
* libguile/init.c: Change so that init just registers an extension,
  later called by foreign.scm.

* libguile/foreign.c (scm_init_foreign): Define constants for the
  various foreign types.

* module/Makefile.am:
* module/system/foreign.scm: New module, for the foreign function
  interface.

module/Makefile.am

@@ -284,6 +284,7 @@ SYSTEM_SOURCES =				\
   system/vm/program.scm				\
   system/vm/trace.scm				\
   system/vm/vm.scm				\
+  system/foreign.scm				\
   system/xref.scm				\
   system/repl/repl.scm				\
   system/repl/common.scm			\

module/system/foreign.scm

@@ -0,0 +1,29 @@
+;;;; 	Copyright (C) 2010 Free Software Foundation, Inc.
+;;;;
+;;;; This library is free software; you can redistribute it and/or
+;;;; modify it under the terms of the GNU Lesser General Public
+;;;; License as published by the Free Software Foundation; either
+;;;; version 2.1 of the License, or (at your option) any later version.
+;;;;
+;;;; This library is distributed in the hope that it will be useful,
+;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;;; Lesser General Public License for more details.
+;;;;
+;;;; You should have received a copy of the GNU Lesser General Public
+;;;; License along with this library; if not, write to the Free Software
+;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+;;;;
+
+
+(define-module (system foreign)
+  #:export (void
+            float double
+            int8 uint8
+            uint16 int16
+            uint32 int32
+            uint64 int64
+
+            foreign-ref foreign-set!))
+
+(load-extension "libguile" "scm_init_foreign")