Terminate unterminated statements + fix some type coercion

[VirtualTim]

I got sick of seeing so many warnings in the generated code, so I thought I'd fix some of the trivial ones.
This may have a very minor positive impact on performance as it should help the optimisers out.

[sbc100]

Where do you see such warnings? What tool produces them? Presumably we can add tests/checks for these to enforce these rules?

[VirtualTim]

They show up in the IDE I'm using - WebStorm.
It actually reports hundreds of warnings, but most of them are due to var usage (lots of duplicate declarations), type coercion (caused by ==), and unused functions/variables.

I'm sure a lot of these are false positives, a function may be unused in the main thread, but used in a worker, but there's at least a few concerning things there. Seeing if (something == 0) makes me a bit uncomfortable, because that's also true if something isn't defined.

I'm sure there's some actual issues there, but I figured I'd just try and fix some of the easy/obvious ones to reduce the noise.

I don't really think this is worth automating, there's just too many false positives at the moment. I guess we could just test a few things, like missing/unnecessary semicolons, but I'm not sure if it's worth the effort.

Edit: It would be nice to restructure things so that there's no undefined variables, because then we could check for that and prevent things like #9025. In my build I'm getting 110 unresolved variables, and I'm sure at least a couple are actual bugs.

[kripken]

Thanks @VirtualTim! Good to clean this stuff up.