Add formspec toolkit and refactor mainmenu to use it

Fix crash on using cursor keys in client menu without selected server
Add support for non fixed size tabviews

builtin/mainmenu/tab_credits.lua

@@ -0,0 +1,62 @@
+--Minetest
+--Copyright (C) 2013 sapier
+--
+--This program 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 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 Lesser General Public License for more details.
+--
+--You should have received a copy of the GNU Lesser General Public License along
+--with this program; if not, write to the Free Software Foundation, Inc.,
+--51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+--------------------------------------------------------------------------------
+
+tab_credits = {
+	name = "credits",
+	caption = fgettext("Credits"),
+	cbf_formspec = function (tabview, name, tabdata)
+			local logofile = defaulttexturedir .. "logo.png"
+			return	"vertlabel[0,-0.5;CREDITS]" ..
+				"label[0.5,3;Minetest " .. core.get_version() .. "]" ..
+				"label[0.5,3.3;http://minetest.net]" ..
+				"image[0.5,1;" .. core.formspec_escape(logofile) .. "]" ..
+				"textlist[3.5,-0.25;8.5,5.8;list_credits;" ..
+				"#FFFF00" .. fgettext("Core Developers") .."," ..
+				"Perttu Ahola (celeron55) <celeron55@gmail.com>,"..
+				"Ryan Kwolek (kwolekr) <kwolekr@minetest.net>,"..
+				"PilzAdam <pilzadam@minetest.net>," ..
+				"Ilya Zhuravlev (xyz) <xyz@minetest.net>,"..
+				"Lisa Milne (darkrose) <lisa@ltmnet.com>,"..
+				"Maciej Kasatkin (RealBadAngel) <mk@realbadangel.pl>,"..
+				"proller <proler@gmail.com>,"..
+				"sfan5 <sfan5@live.de>,"..
+				"kahrl <kahrl@gmx.net>,"..
+				"sapier,"..
+				"ShadowNinja <shadowninja@minetest.net>,"..
+				"Nathanael Courant (Nore/Novatux) <nore@mesecons.net>,"..
+				"BlockMen,"..
+				","..
+				"#FFFF00" .. fgettext("Active Contributors") .. "," ..
+				"Vanessa Ezekowitz (VanessaE) <vanessaezekowitz@gmail.com>,"..
+				"Jurgen Doser (doserj) <jurgen.doser@gmail.com>,"..
+				"Jeija <jeija@mesecons.net>,"..
+				"MirceaKitsune <mirceakitsune@gmail.com>,"..
+				"dannydark <the_skeleton_of_a_child@yahoo.co.uk>,"..
+				"0gb.us <0gb.us@0gb.us>,"..
+				"," ..
+				"#FFFF00" .. fgettext("Previous Contributors") .. "," ..
+				"Guiseppe Bilotta (Oblomov) <guiseppe.bilotta@gmail.com>,"..
+				"Jonathan Neuschafer <j.neuschaefer@gmx.net>,"..
+				"Nils Dagsson Moskopp (erlehmann) <nils@dieweltistgarnichtso.net>,"..
+				"Constantin Wenger (SpeedProg) <constantin.wenger@googlemail.com>,"..
+				"matttpt <matttpt@gmail.com>,"..
+				"JacobF <queatz@gmail.com>,"..
+				";0;true]"
+			end
+	}