handle variable declaration within catch blocks (#1546)

accounts for IE8- scoping

lib/compress.js

@@ -223,6 +223,7 @@ merge(Compressor.prototype, {
 
     AST_Node.DEFMETHOD("reset_opt_flags", function(compressor, rescan){
         var reduce_vars = rescan && compressor.option("reduce_vars");
+        var ie8 = !compressor.option("screw_ie8");
         var safe_ids = [];
         push();
         var suppressor = new TreeWalker(function(node) {
@@ -232,7 +233,7 @@ merge(Compressor.prototype, {
                 d.fixed = false;
             }
         });
-        var tw = new TreeWalker(function(node){
+        var tw = new TreeWalker(function(node, descend){
             if (!(node instanceof AST_Directive || node instanceof AST_Constant)) {
                 node._squeezed = false;
                 node._optimized = false;
@@ -247,6 +248,9 @@ merge(Compressor.prototype, {
                         d.fixed = false;
                     }
                 }
+                if (ie8 && node instanceof AST_SymbolCatch) {
+                    node.definition().fixed = false;
+                }
                 if (node instanceof AST_VarDef) {
                     var d = node.name.definition();
                     if (d.fixed === undefined) {
@@ -301,6 +305,12 @@ merge(Compressor.prototype, {
                     pop();
                     return true;
                 }
+                if (node instanceof AST_Catch) {
+                    push();
+                    descend();
+                    pop();
+                    return true;
+                }
             }
         });
         this.walk(tw);