Exhaustive when on boolean argument. A set of tests.

Compile-time constants are taken into account. #KT-3743 Fixed.

compiler/testData/diagnostics/tests/when/ExhaustiveBooleanComplex.kt

@@ -0,0 +1,8 @@
+// See also: KT-3743
+fun foo(arg: Boolean): String {
+    // Must be exhaustive
+    return when(arg) {
+        2 == 2 -> "truth"
+        2 == 1 -> "falsehood"
+    }
+}