So far in this thread i dont see where you have said any error messages you get. If you are not sure what i mean they try looking in the rc error logs and/or your httpd error logs.
Also reading back through the thread i see it was sort of assumed you are using mysql as your database, is that right?
I´am a little bit confused ...
You posted the correct screenshot with the error message:
Database schema update failed.
DB Schema: NOT OK(Database schema differs)
Missing table 'system'
It´s the same message I get, if I try to update the database with the web installer. In the web installer I have choosen version 0.8.6 to update and pressed the update button ... and the result is:
"Database schema update failed."
What else do you need that you believe that the web installer does not do a correct job?
And yes, I´am using mysql.