assert and non-string errors

[daurnimator]

compat53 should override assert to allow non-string errors.

$ lua5.1 -l compat53
Lua 5.1.5  Copyright (C) 1994-2012 Lua.org, PUC-Rio
> assert(nil, setmetatable({}, { __tostring=function() return "asdf" end }))
stdin:1: bad argument #2 to 'assert' (string expected, got table)
stack traceback:
    [C]: ?
    [C]: in function 'assert'
    stdin:1: in main chunk
    [C]: ?

$ lua5.2 -l compat53
Lua 5.2.4  Copyright (C) 1994-2015 Lua.org, PUC-Rio
> assert(nil, setmetatable({}, { __tostring=function() return "asdf" end }))
stdin:1: bad argument #2 to 'assert' (string expected, got table)
stack traceback:
    [C]: in function 'assert'
    stdin:1: in main chunk
    [C]: in ?

$ lua
Lua 5.3.1  Copyright (C) 1994-2015 Lua.org, PUC-Rio
> assert(nil, setmetatable({}, { __tostring=function() return "asdf" end }))
asdf

Thanks to @Darkstalker for reminding me.

[siffiejoe]

Added in db7cb39.

[daurnimator]

Thanks; prompt as always :D

[daurnimator]

Hey @siffiejoe, can you make a new release with this fix in it? Thanks :)