Sort all namespace files by name prior to assigning names in codegen

This helps to make names of closures etc. stable across compilation, should
also probably help to implement incremental compilation.

No new tests added

compiler/backend/src/org/jetbrains/jet/codegen/binding/CodegenBinding.java

@@ -16,6 +16,7 @@
 
 package org.jetbrains.jet.codegen.binding;
 
+import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.psi.PsiElement;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -34,9 +35,7 @@ import org.jetbrains.jet.lang.types.lang.KotlinBuiltIns;
 import org.jetbrains.jet.util.slicedmap.Slices;
 import org.jetbrains.jet.util.slicedmap.WritableSlice;
 
-import java.util.Collection;
-import java.util.Collections;
-import java.util.HashSet;
+import java.util.*;
 
 import static org.jetbrains.jet.codegen.CodegenUtil.isInterface;
 import static org.jetbrains.jet.lang.resolve.BindingContext.*;
@@ -229,7 +228,23 @@ public class CodegenBinding {
             if (jetFiles != null)
                 answer.addAll(jetFiles);
         }
-        return answer;
+
+        List<JetFile> sortedAnswer = new ArrayList<JetFile>(answer);
+        Collections.sort(sortedAnswer, new Comparator<JetFile>() {
+            @NotNull
+            private String path(JetFile file) {
+                VirtualFile virtualFile = file.getVirtualFile();
+                assert virtualFile != null : "VirtualFile is null for JetFile: " + file.getName();
+                return virtualFile.getPath();
+            }
+
+            @Override
+            public int compare(JetFile first, JetFile second) {
+                return path(first).compareTo(path(second));
+            }
+        });
+
+        return sortedAnswer;
     }
 
     public static boolean isMultiFileNamespace(BindingContext bindingContext, FqName fqName) {