Elgg improvements

[JedMeister]

Testing the v17.0 Elgg release, I noticed a few things that could be improved. They're not "deal breakers", so I'm not going to block the v17.0 release, but they would be good to fix:

• Enable PHP session garbage collection "Configure session.gc_divisor and session.gc_probability in your php.ini." (see https://www.example.com/admin/server)
• ".htaccess rewrite rulesError - Check your .htaccess for the correct rewrite rules" - I had a super quick look at this one and I'm not sure what's wrong?! The Apache conf has AllowOverride All and the htaccess file exists and is readable by www-data. So it should work?!
• Upgrade (on admin page, click "upgrade" button top right corner) fails with an error "Error: Elgg cannot connect to itself to test rewrite rules properly. Check that curl is working and there are no IP restrictions preventing localhost connections."

The first should be easy. The second and third will need some more investigation and my quick searches online suggest that 2 & 3 may be interrelated.