Warn about help option obscured by version option

_registerOption() has been borrowed from deb3bdf in tj#1923.
Watch out for merge conflicts!

lib/command.js

@@ -500,13 +500,33 @@ Expecting one of '${allowedValues.join("', '")}'`);
     return new Option(flags, description);
   }
 
+  /**
+   * Check for option flag conflicts.
+   * Register option if no conflicts found.
+   * Throw otherwise.
+   *
+   * @param {Option} option
+   * @api private
+   */
+
+  _registerOption(option) {
+    this.options.push(option);
+    this._checkForObscuredHelpOption((matchingOptionFlags) => (
+      `Help option '${this._helpOption.flags}' is obscured after adding option '${option.flags}'${matchingOptionFlags.length > 1
+        ? `
+- conflicts with options '${matchingOptionFlags.join("' and '")}'`
+        : ''}`));
+  }
+
   /**
    * Add an option.
    *
    * @param {Option} option
    * @return {Command} `this` command for chaining
    */
   addOption(option) {
+    this._registerOption(option);
+
     const oname = option.name();
     const name = option.attributeName();
 
@@ -521,14 +541,6 @@ Expecting one of '${allowedValues.join("', '")}'`);
       this.setOptionValueWithSource(name, option.defaultValue, 'default');
     }
 
-    // register the option
-    this.options.push(option);
-    this._checkForObscuredHelpOption((matchingOptionFlags) => (
-      `Help option '${this._helpOption.flags}' is obscured after adding option '${option.flags}'${matchingOptionFlags.length > 1
-        ? `
-- conflicts with options '${matchingOptionFlags.join("' and '")}'`
-        : ''}`));
-
     // handler for cli and env supplied values
     const handleOptionValue = (val, invalidValueMessage, valueSource) => {
       // val is null for optional option used without an optional-argument.
@@ -1825,7 +1837,7 @@ Expecting one of '${allowedValues.join("', '")}'`);
     description = description || 'output the version number';
     const versionOption = this.createOption(flags, description);
     this._versionOptionName = versionOption.attributeName();
-    this.options.push(versionOption);
+    this._registerOption(versionOption);
     this.on('option:' + versionOption.name(), () => {
       this._outputConfiguration.writeOut(`${str}\n`);
       this._exit(0, 'commander.version', str);