Define public property 'db_provider' in pdo classes. That is used in various places, especially the installer

program/include/rcube_db.php

@@ -30,6 +30,8 @@
  */
 class rcube_db
 {
+    public $db_provider;
+
     protected $db_dsnw;               // DSN for write operations
     protected $db_dsnr;               // DSN for read operations
     protected $db_connected = false;  // Already connected ?

program/include/rcube_db_mssql.php

@@ -31,6 +31,8 @@
  */
 class rcube_db_mssql extends rcube_db
 {
+    public $db_provider = 'mssql';
+
     /**
      * Driver initialization
      */

program/include/rcube_db_mysql.php

@@ -31,6 +31,8 @@
  */
 class rcube_db_mysql extends rcube_db
 {
+    public $db_provider = 'mysql';
+
     /**
      * Driver initialization/configuration
      */

program/include/rcube_db_pgsql.php

@@ -31,6 +31,8 @@
  */
 class rcube_db_pgsql extends rcube_db
 {
+    public $db_provider = 'postgres';
+
     /**
      * Get last inserted record ID
      *

program/include/rcube_db_sqlite.php

@@ -31,6 +31,8 @@
  */
 class rcube_db_sqlite extends rcube_db
 {
+    public $db_provider = 'sqlite';
+
     /**
      * Database character set
      */

program/include/rcube_db_sqlsrv.php

@@ -31,6 +31,8 @@
  */
 class rcube_db_sqlsrv extends rcube_db
 {
+    public $db_provider = 'mssql';
+
     /**
      * Driver initialization
      */