Fix scoping following try/catch.

test/libsolidity/syntaxTests/tryCatch/scoping.sol

@@ -0,0 +1,10 @@
+contract Test {
+  // This checks a scoping error,
+  // the variable "a" was not visible
+  // at the assignment.
+  function test(address _ext) external {
+    try Test(_ext).test(_ext) {} catch {}
+    uint a = 1;
+    a = 3;
+  }
+}