Expose love.event.poll_i

Now love.event.poll just returns love.event.poll_i, instead of returning a new
c function every call. This means love no longer creates garbage each frame
(with an empty project).

See pull request #81 for details, and an alternative fix. Thanks @bjornbytes
for the pull request, and for finding this issue.

Note: in the pull request I also mentioned love.filesystem.lines/File:lines. I
haven't "fixed" those since they use actual closures.

--HG--
branch : minor

src/modules/event/wrap_Event.lua

@@ -0,0 +1,30 @@
+R"luastring"--(
+-- DO NOT REMOVE THE ABOVE LINE. It is used to load this file as a C++ string.
+-- There is a matching delimiter at the bottom of the file.
+
+--[[
+Copyright (c) 2006-2017 LOVE Development Team
+
+This software is provided 'as-is', without any express or implied
+warranty.  In no event will the authors be held liable for any damages
+arising from the use of this software.
+
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it
+freely, subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not
+claim that you wrote the original software. If you use this software
+in a product, an acknowledgment in the product documentation would be
+appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be
+misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+--]]
+
+function love.event.poll()
+	return love.event.poll_i
+end
+
+-- DO NOT REMOVE THE NEXT LINE. It is used to load this file as a C++ string.
+--)luastring"--"