title: Strange Mongoose schema.js error - `options` may not be used as a schema pathname
body: <p>In my schema, if I have <code>options</code> in <code>metrics : [ { options : {} } ]</code>then I get:</p>
  
  <pre><code>/home/one/cloudimageshare-monitoring/project/node_modules/mongoose/lib/schema.js:282
      throw new Error("`" + path + "` may not be used as a schema pathname");
            ^
  Error: `options` may not be used as a schema pathname
  </code></pre>
  
  <p>But if change <code>options</code> to any other word... like <code>qoptions</code>....then the error goes away. Why is this happening?</p>
  
  <pre><code>var mongoose = require('mongoose');
  var Schema = mongoose.Schema;
  
  var FilesystemSchema = new mongoose.Schema({
      timeStamp : { type : Date, index: true },
      avaiable : Boolean,
      status : String,
      metrics : [
          { options : {
                  data : String,
                  type : String,
                  unit : String
                 }
          },
          { freeFiles : {
                data : Number,
                type : String,
                unit : String
               }
          },
          { total : {
                data : Number,
                type : String,
                unit : String
               }
          },
          { avail : {
                data : Number,
                type : String,
                unit : String
               }
          },
          { free : {
                data : Number,
                type : String,
                unit : String
               }
          },
          { files : {
                data : Number,
                type : String,
                unit : String
               }
          },
          { used : {
                data : Number,
                type : String,
                unit : String
               }
          }
   ]   
  });
  
  module.exports = FilesystemSchema;
  </code></pre>