Treat debug: true debug: ""

Supports passing `true` for `debug` in `mangle_properties`. Added test
case to verify this behavior.

lib/propmangle.js

@@ -103,9 +103,13 @@ function mangle_properties(ast, options) {
     var ignore_quoted = options.ignore_quoted;
     
     // note debug is either false (disabled), or a string of the debug suffix to use (enabled).
-    // note debug may be enabled as an empty string, which is falsey.
+    // note debug may be enabled as an empty string, which is falsey. Also treat passing 'true'
+    // the same as passing an empty string.
     var debug = (options.debug !== false);
-    var debug_name_suffix = debug ? options.debug : null;
+    var debug_name_suffix;
+    if (debug) {
+        debug_name_suffix = (options.debug === true ? "" : options.debug);
+    }
 
     var names_to_mangle = [];
     var unmangleable = [];

test/compress/properties.js

@@ -157,6 +157,20 @@ mangle_debug: {
     }
 }
 
+mangle_debug_true: {
+    mangle_props = {
+        debug: true
+    };
+    input: {
+        a.foo = "bar";
+        x = { baz: "ban" };
+    }
+    expect: {
+        a._$foo$_ = "bar";
+        x = { _$baz$_: "ban" };
+    }
+}
+
 mangle_debug_suffix: {
     mangle_props = {
         debug: "XYZ"