Why do lua_open* functions leave stuff on the stack?

["Curt Carpenter" <curtc@...>]

They all appear to leave a table on the stack. This really screwed me up
when tracking down a stack balance issue.

What's the table? Docs mention nothing about a table on the stack after
calling these.

They all seem to push the same table. luaopen_io pushes it *3* times.

Thanks,

Curt