Add Oracle driver check in Installer

installer/check.php

@@ -67,6 +67,7 @@ $source_urls = array(
     'DOM'       => 'http://www.php.net/manual/en/book.dom.php',
     'Intl'      => 'http://www.php.net/manual/en/book.intl.php',
     'Exif'      => 'http://www.php.net/manual/en/book.exif.php',
+    'oci8'      => 'http://www.php.net/manual/en/book.oci8.php',
     'PDO'       => 'http://www.php.net/manual/en/book.pdo.php',
     'pdo_mysql'   => 'http://www.php.net/manual/en/ref.pdo-mysql.php',
     'pdo_pgsql'   => 'http://www.php.net/manual/en/ref.pdo-pgsql.php',

program/include/rcmail_install.php

@@ -55,6 +55,7 @@ class rcmail_install
     'SQLite (v2)'         => 'pdo_sqlite2',
     'SQL Server (SQLSRV)' => 'pdo_sqlsrv',
     'SQL Server (DBLIB)'  => 'pdo_dblib',
+    'Oracle'              => 'oci8',
   );