Smart casts for local variables not captured in a closure and not changed in a loop, see #KT-3175.

isLocalVariable added. Assignment / initialization analysis.
Control whether a variable is changed in a loop at the beginning and at the end of the loop.
Control whether a variable is captured in a closure. #KT-3175  Fixed. #KT-2266  Fixed.
Tests for variable null safety and for variables is/as operations.
Loop / closure / variable property tests are included.
Old tests changed in accordance with KT-3175. In particular, all three of testSmartcastImpossible were fixed.

compiler/testData/diagnostics/tests/smartCasts/inference/kt4009.kt

@@ -10,10 +10,11 @@ fun foo1(e: PsiElement) {
     var first = true
     while (current != null) {
         if (current is JetExpression && first) {
-            println(current!!.getText()) // error: smart cast not possible. But it's not needed in fact!
+            // Smartcast is possible here
+            println(<!DEBUG_INFO_SMARTCAST!>current<!>.getText())
         }
 
-        current = current?.getParent()
+        current = <!DEBUG_INFO_SMARTCAST!>current<!>.getParent()
     }
 }