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/controlFlowAnalysis/kt2845.kt

@@ -7,7 +7,8 @@ private fun doTest() : Int {
     var list : MutableList<Int>? ;
     try {
         list = ArrayList()
-        list?.add(3)
+        // Not-null was just assigned to the list
+        <!DEBUG_INFO_SMARTCAST!>list<!>.add(3)
         return 0 ;
     }
     finally {