MDL-29322 instruct oracle to use current NLS char size when creating VARCHAR2 fields

This solves problems on servers with default configuration where VARCHAR2 sizes are specified in bytes. Also add more reserved words.

lib/ddl/oracle_sql_generator.php

@@ -163,11 +163,14 @@ class oracle_sql_generator extends sql_generator {
                 }
                 break;
             case XMLDB_TYPE_CHAR:
+                // Do not use NVARCHAR2 here because it has hardcoded 1333 char limit,
+                // VARCHAR2 allows us to create larger fields that error out later during runtime
+                // only when too many non-ascii utf-8 chars present.
                 $dbtype = 'VARCHAR2';
                 if (empty($xmldb_length)) {
                     $xmldb_length='255';
                 }
-                $dbtype .= '(' . $xmldb_length . ')';
+                $dbtype .= '(' . $xmldb_length . ' CHAR)'; // CHAR is required because BYTE is the default
                 break;
             case XMLDB_TYPE_TEXT:
                 $dbtype = 'CLOB';
@@ -670,8 +673,8 @@ class oracle_sql_generator extends sql_generator {
             'increment', 'index', 'initial', 'insert',
             'integer', 'intersect', 'into', 'is', 'level',
             'like', 'lock', 'long', 'maxextents', 'minus',
-            'mlslabel', 'mode', 'modify', 'noaudit',
-            'nocompress', 'not', 'nowait', 'null', 'number',
+            'mlslabel', 'mode', 'modify', 'nchar', 'nclob', 'noaudit',
+            'nocompress', 'not', 'nowait', 'null', 'number', 'nvarchar2',
             'of', 'offline', 'on', 'online', 'option', 'or',
             'order', 'pctfree', 'prior', 'privileges',
             'public', 'raw', 'rename', 'resource', 'revoke',