Fix symlinked plugin directories not loading

Due to a bug in LÖVE that goes down to PhysFS[1], a symlinked directory
isn't recognized as a directory, so symlinked plugin directories won't
be loaded.

To fix this, just load it anyway if it's a symlink. If the symlink turns
out to be a file, that's harmless because it will just be loaded as an
unknown plugin that does nothing.

[1]: love2d/love#1938

Source/love11compat.lua

@@ -37,6 +37,10 @@ love.filesystem.isFile = function(filename)
 	return love.filesystem.getInfo(filename, "file") ~= nil
 end
 
+love.filesystem.isSymlink = function(filename)
+	return love.filesystem.getInfo(filename, "symlink") ~= nil
+end
+
 love.filesystem.getLastModified = function(filename)
 	local info = love.filesystem.getInfo(filename)
 	if info == nil then return nil end

Source/plugins.lua

@@ -69,7 +69,9 @@ function loadplugins()
 		folders = love.filesystem.getDirectoryItems("plugins")
 
 		for k,v in pairs(folders) do
-			if love.filesystem.isDirectory("plugins/" .. v) or v:sub(-4, -1) == ".zip" then
+			if love.filesystem.isDirectory("plugins/" .. v)
+			or (love_version_meets(9, 2) and love.filesystem.isSymlink("plugins/" .. v))
+			or v:sub(-4, -1) == ".zip" then
 				-- This is a plugin folder/zip, neat! But if it's a zip, then we first need to mount it.
 				local pluginpath, pluginname