Proper error reporting when a package name redeclares something, wrt the package name occurring in multiple files

See MultiFilePackageRedeclaration.jet test

compiler/testData/diagnostics/tests/redeclarations/MultiFilePackageRedeclaration.jet

@@ -0,0 +1,7 @@
+// FILE: f.kt
+package a
+class <!REDECLARATION!>b<!> {}
+// FILE: f.kt
+package a.<!REDECLARATION!>b<!>
+// FILE: f.kt
+package a.<!REDECLARATION!>b<!>

compiler/testData/diagnostics/tests/redeclarations/Redeclarations.jet

@@ -0,0 +1,15 @@
+// FILE: f.kt
+package redeclarations
+  object <!REDECLARATION!>A<!> {
+    val x : Int = 0
+
+    val A = 1
+  }
+
+  class <!REDECLARATION!>A<!> {}
+
+  val <!REDECLARATION!>A<!> = 1
+
+// FILE: f.kt
+  package redeclarations.<!REDECLARATION!>A<!>
+    class A {}