Rewrite generated calls to Objects.requireNonNull()

[cushon]

In JDK 8 and below, javac generates synthetic null-checks by calling Object.getClass. Starting in JDK 9, Objects.requireNonNull() is used if it is available (see JDK-8074306).

This prevents retrolambda users from compiling code with JDK9 and running it on JDK6 or below, since java.util.Objects was introduced in JDK7.

When targeting JDK < 7, retrolambda should rewrite the generated calls to requireNonNull.

[luontola]

Cool. Thanks about telling what JDK 9 does. I haven't yet tried using it. I'll try to get some time to update Retrolambda this month.

[luontola]

This is included in Retrolambda 2.2.0