IDEA-130745 Incorrect auto cast after completion

* when merging dfa states, check that they're really equal after stripping complementary facts (there might be additional info in subclasses)
* merge in separate groups in one go

java/java-tests/testData/codeInsight/completion/normal/DontCastPartiallyInstanceofedQualifier.java

@@ -0,0 +1,16 @@
+public abstract class Zzza {
+
+    abstract Object getFoo();
+
+    void foo(Zzza other) {
+      int a;
+      if (other.getFoo() instanceof String) {
+        a = 1;
+      } else {
+        a = 2;
+      }
+      other.getFoo().subst<caret>
+    }
+
+
+}