backend: add tests for try-catch-finally and throwing exceptions

also add some tests for bugs with unreachable code handling and variables

backend.native/tests/codegen/try/finally1.kt

@@ -0,0 +1,10 @@
+fun main(args : Array<String>) {
+
+    try {
+        println("Try")
+    } finally {
+        println("Finally")
+    }
+
+    println("Done")
+}