Rename namespace class to {package.name}Package

Conflicts:

	compiler/jet.as.java.psi/src/org/jetbrains/jet/asJava/JavaElementFinder.java

compiler/testData/writeSignature/VarargCharSequence.kt

@@ -1,6 +1,6 @@
 fun foo(vararg tail: java.lang.CharSequence) = 1
 
-// method: namespace::foo
+// method: _DefaultPackage::foo
 // jvm signature:     ([Ljava/lang/CharSequence;)I
 // generic signature: null
 // kotlin signature:  ([Mjava/lang/CharSequence;)I // TODO: need to skip kotlin signature