[folks] Add the MaybeBool type.

[Travis Reitter <treitter src gnome org>]

commit 446ba7bed51d425db48f6efd73c507b7f62d7d4d
Author: Travis Reitter <travis reitter collabora co uk>
Date:   Thu Oct 7 12:51:22 2010 -0700

    Add the MaybeBool type.

 folks/Makefile.am |    1 +
 folks/types.vala  |   37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 0 deletions(-)
---
diff --git a/folks/Makefile.am b/folks/Makefile.am
index bccb3a3..1d9bf73 100644
--- a/folks/Makefile.am
+++ b/folks/Makefile.am
@@ -24,6 +24,7 @@ folks_valasources = \
 	persona.vala \
 	persona-store.vala \
 	presence.vala \
+	types.vala \
 	debug.vala \
 	$(NULL)
 
diff --git a/folks/types.vala b/folks/types.vala
new file mode 100644
index 0000000..ba93480
--- /dev/null
+++ b/folks/types.vala
@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2010 Collabora Ltd.
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors:
+ *       Travis Reitter <travis reitter collabora co uk>
+ */
+
+using GLib;
+
+namespace Folks
+{
+  /**
+   * A 'boolean' type that has a distinct 'unset' state.
+   */
+  public static enum MaybeBool
+    {
+      /* This value is explicitly unset. */
+      UNSET = 0,
+      /* False (this value was set from its default of UNSET). */
+      FALSE = 1,
+      /* True (this value was set from its default of UNSET). */
+      TRUE = 2,
+    }
+}