Description:
------------
In PHP 7, `assert` became a language construct and cannot be redefined as a user function. Typically language constructs can't be imported via use statements, however, it seems that `assert` can be imported via a use statement. I'm not sure if this is intentional or not for BC purposes. PHP throws a ParseError when trying to import other language constructs, such as `isset`, so I would expect importing `assert` to throw as well.

Test script:
---------------
// Works, unexpectedly
namespace Foo {
    use function assert;
}

// Doesn't work, as expected
namespace Foo {
    use function isset;
}