[ticket/16741] Specific DBs fixes

MSSQL:
- Fix bool type
- Fix comparator
- Drop Default constraint before deleting column
- Rename Default constraint to use phpBB's names
- Re-create the indices when changing the type of one column
- Uses varchar instead of varbinary

PostgreSQL:
- Creates auto increment sequences by hand instead of using serial
  in order to use phpBB's names
- Drop constraint on unique / primary indices

Oracle:
- Rename indices to use phpBB's names
- Fix string not null behaviour
- Fix broken regex in Oracle driver
- Handle to long indices on Oracle
- Rename auto_increment trigger and sequence
- Automatically lowercase keys in assoc results

PHPBB3-16741

phpBB/phpbb/db/tools/mssql.php

@@ -19,6 +19,6 @@ namespace phpbb\db\tools;
  *
  * @deprecated 4.0.0-a1
  */
-class mssql extends tools
+class mssql extends doctrine
 {
 }

phpBB/phpbb/db/tools/postgres.php

@@ -19,6 +19,6 @@ namespace phpbb\db\tools;
  *
  * @deprecated 4.0.0-a1
  */
-class postgres extends tools
+class postgres extends doctrine
 {
 }