fix for #82: missing ldap_knownname

ldap_knownname has no default value in the db schema, but wasn't being
set, resulting in an error. Following the behavior of upgrade.php, I've
set this to the same value as ldap_host. However, I can't find any
evidence of ldap_knownname actually being used anywhere, so is it even
needed?
Fix for #82: undefined database_type

The database.php template does not set database_type, which is needed
during installation.

Additionally, since all of the database_* values are set as properties
of $xerte_toolkits_site at the top of the file, I updated the code
further down to use those values instead of pulling from _POST/_SESSION,
etc again.
Merge pull request #86 from usernamenumber/ldap_knownname

Fixes for #82