2.9 regression: Java interop: in signature, primitive types become Object when generics are also present

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as of r24390:

  ~> scala/dists/latest/bin/scala -version
Scala code runner version 2.9.0.r24390-b20110306074150 -- Copyright 2002-2011, LAMP/EPFL
  ~> cat S.scala                                                      
object S { def foo(x: Class[_ <: AnyRef]) = 0 }
  ~> scala/dists/latest/bin/scalaC S.scala
  ~> cat J.java                                                         
class J {
	int bar() { return S.foo(String.class) ; }
}
  ~> javac -classpath .:scala/dists/latest/lib/scala-library.jar J.java
J.java:2: incompatible types
found   : java.lang.Object
required: int
	int bar() { return S.foo(String.class) ; }
	                        ^
1 error

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Imported From: https://issues.scala-lang.org/browse/SI-4317?orig=1
Reporter: @SethTisue

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@SethTisue said:
a new chapter in the saga of #3249 / #3486 / #4238 / #4316

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@paulp said:
(In r24391) Another corner involving generic signatures and java interop
flushed out by seth tisue. Keep that detector fired up seth or the
rebel alliance will surely be crushed. (In fact, I nominate you
to write a test suite!) Closes #4317, no review.

[scabug]

@SethTisue said:
compile-time is good now, but runtime's another story:

  ~> scala/dists/latest/bin/scala -version                             
Scala code runner version 2.9.0.r24391-b20110306095638 -- Copyright 2002-2011, LAMP/EPFL
  ~> cat S.scala
object S { def foo(x: Class[_ <: AnyRef], y: Int) = 99 }
  ~> scala/dists/latest/bin/scalac S.scala                             
  ~> cat J.java
public class J {
	public static void main(String[] args) {
		int b = S.foo(String.class, 0);
		System.out.println(b);
	}
}
  ~> javac -classpath .:scala/dists/latest/lib/scala-library.jar J.java
  ~> java -classpath .:scala/dists/latest/lib/scala-library.jar J      
Exception in thread "main" java.lang.NoSuchMethodError: S.foo(Ljava/lang/Class;Ljava/lang/Object;)I
	at J.main(J.java:3)

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@paulp said:
(In r24399) More signature fixes and tests and generally being more sophisticated
about our primitive squashing. These signatures belong in world-class
museums but we are their shepherds for now. Closes #4317, no review.