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.

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/DataFlowInfoUtilForCompletion.kt

@@ -24,7 +24,7 @@ import org.jetbrains.kotlin.descriptors.PackageViewDescriptor
 
 fun renderDataFlowValue(value: DataFlowValue): String? {
     // If it is not a stable identifier, there's no point in rendering it
-    if (!value.isStableIdentifier()) return null
+    if (!value.isStableIdentifier() && !value.isLocalVariable()) return null
 
     fun renderId(id: Any?): String? {
         return when (id) {