Fix index creation for MySQL.

src/java/com/samskivert/depot/impl/BuildVisitor.java

@@ -545,9 +545,7 @@ public abstract class BuildVisitor implements ExpressionVisitor
             }
             comma = true;
 
-            _builder.append("(");
-            field.left.accept(this);
-            _builder.append(")");
+            appendIndexComponent(field.left);
             if (field.right == Order.DESC) {
                 // ascending is default, print nothing unless explicitly descending
                 _builder.append(" desc");
@@ -704,6 +702,15 @@ public abstract class BuildVisitor implements ExpressionVisitor
             "Persistent field has no definition [class=" + type + ", field=" + field + "]");
     }
 
+    // output one of potentially many fields in an index expression
+    protected void appendIndexComponent (SQLExpression expression)
+    {
+        // the standard builder wraps each field in its own parens
+        _builder.append("(");
+        expression.accept(this);
+        _builder.append(")");
+    }
+
     protected BuildVisitor (DepotTypes types)
     {
         _types = types;

src/java/com/samskivert/depot/impl/MySQLBuilder.java

@@ -140,6 +140,13 @@ public class MySQLBuilder
             _builder.append(field);
         }
 
+        @Override
+        protected void appendIndexComponent (SQLExpression expression)
+        {
+            // MySQL is never given complex expressions and hates parens, so just recurse
+            expression.accept(this);
+        }
+
         protected void renderMatch (FullText fullText)
         {
             _builder.append("match(");