#376 USE_DB_SESSION is badly handled

[François Beretti]

The USE_DB_SESSION variable should be set to false when
using a flat file database, as said in bug 987757.

If it is not, a lot of php errors is displayed when
using the wiki

But setting this in config.ini has no effect, because
USE_DB_SESSION is not listed in the _IC_VALID_BOOL
array in lib/IniConfig.php

You just have to add it in the end of the array to
solve the problem.

Moreover, it would be a good idea to document it in
config.ini

Or maybe to automatically set it to false when the
database backend is 'file'

Regards,

François Beretti