Re: lily: fix some type conversion warnings (issue 557190043 by address@hidden)

[hanwenn]

> I don't like this methodology, what's the difference over disabling
> -Wconversion

My selfish is reason is that it gets the warnings out of the way of
whomever is not interested in fixing casts, including myself.

The reason why this methodology is better approach overall is that it
actually prevents from more dubious casts being added.

Right now, if I add another erroneous cast, it will generate a warning
that looks similar to the zillions of warnings I already ignore, and it
will need an eagle-eyed reviewer to catch the problem. 

If the base compile is free of warnings, we can add -Werror to the
compile, and any new errors will cause a failure in our CI, which is a
much better way of preventing regressions.

https://codereview.appspot.com/557190043/