Rename love.errhand to love.errorhandler (see issue #573).

love.errhand will still be called if love.errorhandler doesn't exist, and love defines love.errhand by default rather than love.errorhandler, to prevent hard-to-diagnose problems with existing code that defines love.errhand.

--HG--
branch : minor

src/scripts/boot.lua

@@ -716,7 +716,7 @@ function love.errhand(msg)
 end
 
 local function deferErrhand(...)
-	local handler = love.errhand or error_printer
+	local handler = love.errorhandler or love.errhand or error_printer
 	return handler(...)
 end