extend function inlining safety checks

[alexlamsl]

@kzc this is the final version of #2427 (comment)

[kzc]

Fantastic.

Could you please add this correctly working test?

$ cat scope1.js 
function x() {
    y();
}
function y() {
    console.log(1);
}
function z() {
    function y() {
        console.log(2);
    }
    x();
    y();
}
z();
z();

$ cat scope1.js | bin/uglifyjs -c toplevel,passes=2
function z(){console.log(1),console.log(2)}z(),z();

[alexlamsl]

#2430 (comment) added in af7bb57

[kzc]

I swear you code faster than I can think.

[alexlamsl]

In which case, I shall get some sleep while you catch up... 👻