backend: Use simple DFS during closure building.

Now closure builder can contain includes. Includes
are another builders which closures must be added
to the building one.
Includes are:

For function closure:
	call targets (including constructors)
	callable reference targets

For class:
	all children declarations
	call targets (including constructors)
        callable reference targets

For constructor:
	call and callable reference targets
	delegating constructor call target
	constructing class closure

backend.native/tests/codegen/localClass/localFunctionCallFromLocalClass.kt

@@ -0,0 +1,14 @@
+fun main(args : Array<String>) {
+    var x = 1
+    fun local1() {
+        x++
+    }
+
+    class A {
+        fun bar() {
+            local1()
+        }
+    }
+    A().bar()
+    println("OK")
+}

backend.native/tests/codegen/localClass/localFunctionInLocalClass.kt

@@ -0,0 +1,21 @@
+fun main(args : Array<String>) {
+    var x = 0
+    class A {
+        fun bar() {
+            fun local() {
+                class B {
+                    fun baz() {
+                        fun local2() {
+                            x++
+                        }
+                        local2()
+                    }
+                }
+                B().baz()
+            }
+            local()
+        }
+    }
+    A().bar()
+    println("OK")
+}