ruby: Don't segfault if callbacks throw exceptions (RHBZ#664558).

(Thanks Chris Lalancette).

See:
https://bugzilla.redhat.com/show_bug.cgi?id=664558#c6

ruby/tests/tc_rhbz664558c6.rb

@@ -0,0 +1,48 @@
+# libguestfs Ruby bindings -*- ruby -*-
+# Copyright (C) 2011 Red Hat Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+# Test that throwing an exception in a callback doesn't cause
+# the interpreter to segfault.  See:
+# https://bugzilla.redhat.com/show_bug.cgi?id=664558#c6
+
+require 'test/unit'
+$:.unshift(File::join(File::dirname(__FILE__), "..", "lib"))
+$:.unshift(File::join(File::dirname(__FILE__), "..", "ext", "guestfs"))
+require 'guestfs'
+
+class TestLoad < Test::Unit::TestCase
+  def test_rhbz664558c6
+    g = Guestfs::create()
+
+    close_invoked = 0
+    close = Proc.new {| event, event_handle, buf, array |
+      close_invoked += 1
+      # Raising an exception used to cause the interpreter to
+      # segfault.  It should just cause an error message to be
+      # printed on stderr.
+      raise "ignore this error"
+    }
+    g.set_event_callback(close, Guestfs::EVENT_CLOSE)
+
+    # This should call the close callback.
+    g.close()
+
+    if close_invoked != 1
+      raise "close_invoked should be 1"
+    end
+  end
+end