Fix #87: security helper converted into component and improved

Fix #87: security helper improvement

Migrated from #4052
Can we change the default to `"pbkdf2"`? I know it won't work in PHP 5.4 but the exception thrown alerts the developer to the security question and explains how to fix it. I think this is a good way to nudge people to 5.5 if they want to use key stretching.