Upgrade 5.7.3 -> 5.7.5.3 problems

I ran into some troubles upgrading an old testing site. Maybe someone else encounters the same problem, so here's what I found for future reference.

There were a few problems stacking up and interfering.

• the server ran out of memory when downloading and unzipping a new version, therefore, the /tmp was rerouted resulting in new problems with session writing.
• 'is_dir(): open_basedir restriction in effect. File(dev/shm/) is not within the allowed path(s)' error
• databases error's occured due to unfinished installs or server problems

links:

http://stackoverflow.com/questions/1846882/open-ba...

http://www.concrete5.org/community/forums/installa...

https://www.concrete5.org/documentation/how-tos/de...

http://documentation.concrete5.org/tutorials/how-t...

concrete5 github: #2581, #520

Here's what did work in the end:

1. don't upgrade with the build in tools (concrete5, installatron), but do a manual upgrade
2. write sessions to database instead of files. (to trick the dev/shm/ error). Add to /application/config/concrete.php:

return array(      'session' => array(          'handler' => 'database'      )  );

3. normal manual upgrade according to http://documentation.concrete5.org/tutorials/how-t...