Compiler warning/error for duplicate variable declaration

[Domingo Alvarez Duarte <mingodad@...>]

Hello !

Doing several conversions from Lua to LJS 
https://github.com/mingodad/ljs I found a frequent usage of duplicate 
variable declarations that make the code hard to understand/port and in 
some cases it causes bugs that pass unnoticed like this one in luajit 
https://www.freelists.org/post/luajit/Duplicated-variable-declaration-BUG .

In LJS I created a compiler warning/error that catch those problems at 
compile time see patches that can be applied to Lua in 
http://lua-users.org/wiki/LuaPowerPatches .

I hope more people would be aware of this problem and that it could be 
eliminated by using a compiler help like the one proposed.

If you have any code in Lua that you care I invite you to compile a 
patched version of lua and try run your code with it to see if you have 
this problem in your code.

Any comment/suggestion is welcome !

Cheers !