CRM_Utils_Check_Env::checkMysqlTime - Be more forgiving

Per lcdweb, differences of 1-2 min are acceptable. This check was
originally created because some PHP/MySQL systems have different
TZ's and show differences of several hours.
Merge pull request #3399 from totten/4.4-time-threshold

CRM_Utils_Check_Env::checkMysqlTime - Be more forgiving