WordPress Posts Widget: Fix an intermittent fatal error
WordPress Posts Widget: Add HTML comment to end of widget
WordPress Posts Widget: Fix PHP coding style

Also use double quotes around HTML attributes.
WordPress Posts Widget: Normalize www

When a user enters a site with a www. that doesn't exist, but the site
without the www. does exist, use the latter.
WordPress Posts Widget: Don't display more posts than exist
WordPress Posts Widget: Fix transient bugs

- `get_transient` and `set_transient` do not take a namespace parameter
- expiring transients have a name length maximum of 45 characters