powerset does not generate a power set

[Teguh Hofstee]

Despite its name, powerset does not actually create a power set. For example, the documentation states when given the set {1,2,3}, returns {{1},{2},{3},{1,2},{2,3},{1,2,3}} however the power set of {1,2,3} is actually {{},{1},{2},{3},{1,2},{1,3},{2,3},{1,2,3}}. Specifically {} and {1,3} are missing in this case.

[Roland]

Thanks @THofstee, good catch!

However, I cannot include this pull request, since the correct implementation you just provided is only valid with Lua 5.3 (it uses bit operators, which are not available with Lua 5.1 and Lua 5.2).

Since I want to preserve compatibility with previous versions of Lua, I will go with another proposal. Less faster though, but correct.