factor copy-tree and cons-source out of eval.[ch]

* libguile.h:
* libguile/Makefile.am
* libguile/init.c (scm_i_init_guile): Add trees.[ch] to the build.

* libguile/eval.c:
* libguile/eval.h: Remove scm_copy_tree and scm_cons_source...

* libguile/trees.h:
* libguile/trees.c:
* libguile/srcprop.h:
* libguile/srcprop.c: ... factoring them out here and here,
  respectively.

* test-suite/tests/eval.test ("memoization"): Change expected exception
  for circular data structures, given new copy-tree location.

libguile/trees.h

@@ -0,0 +1,45 @@
+/* classes: h_files */
+
+#ifndef SCM_TREES_H
+#define SCM_TREES_H
+
+/* Copyright (C) 2009
+ * 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 3 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
+ */
+
+
+
+#include "libguile/__scm.h"
+
+
+
+SCM_API SCM scm_copy_tree (SCM obj);
+
+
+
+/* Guile internal functions */
+
+SCM_INTERNAL void scm_init_trees (void);
+
+#endif  /* SCM_TREES_H */
+
+/*
+  Local Variables:
+  c-file-style: "gnu"
+  End:
+*/