Implement try/catch/throw in optimizing.

- We currently don't run optimizations in the presence of a try/catch.
- We therefore implement Quick's mapping table.
- Also fix a missing null check on array-length.

Change-Id: I6917dfcb868e75c1cf6eff32b7cbb60b6cfbd68f
diff --git a/test/421-exceptions/info.txt b/test/421-exceptions/info.txt
new file mode 100644
index 0000000..bdec67e
--- /dev/null
+++ b/test/421-exceptions/info.txt
@@ -0,0 +1 @@
+Simple test for try/catch/throw.