Include gender fields in Contact get spec

This is similar to http://issues.civicrm.org/jira/browse/CRM-13223

Previously, if one issued the following request, the gender-related fields would not be included:
/civicrm/ajax/rest?entity=Contact&action=get&id=3&return=gender

Now, with the patch found below, the above query returns the gender fields.

diff --git a/api/v3/Contact.php b/api/v3/Contact.php
index b42f968..8330f31 100644
— a/api/v3/Contact.php
+++ b/api/v3/Contact.php
@@ -226,6 +226,10 @@ function _civicrm_api3_contact_get_spec(&$params) {
$params['email_id']['title'] = 'Primary Email ID';
$params['email']['title'] = 'Primary Email';
$params['on_hold']['title'] = 'Primary Email On Hold';
+ $params['gender_id']['title'] = 'Gender ID';
+ $params['gender']['title'] = 'Gender';
$params['im']['title'] = 'Primary Instant Messanger';
$params['im_id']['title'] = 'Primary Instant Messanger ID';
$params['group_id']['title'] = 'Group Memberships (filter)';