1.x: javac 9 compatibility fixes

[akarnokd]

The type inference of javac in JDK 9 has been changed in an incompatible way, marking many generics-related code invalid.

The most common problems:

• The inference calculates Observable<? extends T> but from its perspective, a call to subscribe() with a Subscriber<T> is ambiguous as it matches subscribe(Observer<? super T>) and subscribe(Subscriber<? super T>). Somehow, the more specific class is not considered as a valid choice. Downcasting to Observable<T> fixes the error.
• A<?>[] no longer accepts A<Ti> elements, requires the use of raw types to get around

The tests appear to compile fine.

Note that I couldn't find a working IDE for JDK 9 and had to revert to command line trickery:

@echo off

dir /s /B src\main\java\rx\*.java > sources.txt
dir /s /B src\test\java\rx\*.java >> sources.txt

"c:\program files\java\jdk-9\bin\javac.exe" -cp C:/temp/rx/junit.jar;C:/temp/rx/mockito.jar @sources.txt 

del sources.txt

[artem-zinnatullin]

👍

// @akarnokd maybe report "incorrect" behavior of JDK9 compiler to OpenJDK issue tracker?

[akarnokd]

There were reports such as this before. Bottom line is that they are fine with their breaking change.

[stevegury]

👍