Suppress useless warnings

[Jolanrensen]

300 is enough, isn't it?

We should suppress warnings that are dealt with, like "Unchecked cast", so we can see new warnings that are actually useful, like "This code uses error suppression for 'INAPPLICABLE_JVM_NAME'. While it might compile and work, the compiler behavior is UNSPECIFIED and WON'T BE PRESERVED."