Bug 9085 - Installer will not run with DEBUG set

Bug 9085 - Installer will not run with DEBUG set

This is due to raising all db errors combined with the fact that attempts
to make selections from a non-existent systempreferences table raises db errors.

The installer should run even with DEBUG set, otherwise dropping and recreating
a development database becomes somewhat of a chore. This patch adds code to
check for the existence of the systempreferece table. If the table exists, then
RaiseError is enabled on the database handle. Otherwise it is disabled to allow
the installer to run without throwing an error.

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
The installer can now be run both with and without DEBUG set.

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>