gen_stub: Also verify implementation-alias

[nikic]

This makes --verify also check @implementation-alias. Failures are ignored using @no-verify instead. Some mistakes have been made that would have been caught by this...

There is one remaining failure:

SplFileObject::__toString() and SplFileObject::fgets() must have the same return type

Another example of great terrible API design in SPL. Converting a file into a string returns ... the current line. Which can return false. Probably the alias here needs to be dropped and we should return "" instead of false.

[nikic]

@kocsismate What do you think about this?

[nikic]

The SplFileObject issue is fixed by f2364f3. It turns out that fgets() can't actually return false here, so we can make the return types line up.

[kocsismate]

Sounds like a good idea! :)