Do not use length specifiers in a primary key

When I try to enable block_class module (http://drupal.org/project/block_class), the following error occurs:

PDOException: SQLSTATE[42000]: [Microsoft][SQL Server Native Client 10.0][SQL Server]Cannot use duplicate column names in index. Column name 'Array' listed more than once.: CREATE TABLE [{block_class}] ( [module] nvarchar(255) NOT NULL CONSTRAINT {block_class}_module_df DEFAULT '', [delta] nvarchar(255) NOT NULL CONSTRAINT {block_class}_delta_df DEFAULT '', [css_class] nvarchar(255) NOT NULL CONSTRAINT {block_class}_css_class_df DEFAULT '', CONSTRAINT {block_class}_pkey PRIMARY KEY CLUSTERED ([Array], [Array]) ); Array ( ) in db_create_table() (line 2686 of D:\work\jandenul\includes\database\database.inc).

It is caused by wrong installation schema handling. If I'm not mistaking, Microsoft SQL doesn't allow explicitly set index prefix length. As it is specified in docs (http://drupal.org/node/146939):

'primary key': An array of one or more key column specifers that form the primary key.
A key column specifier is either a string naming a field or an array of two elements, a string naming a field and an integer prefix length. If a prefix length is specified, only that many bytes or characters of the named field are used as part of the key. If the database engine does not support this optimization, the prefix length is ignored.

I have no time to provide consistent patch, but will suggest a fix right here (apply to sqlsrv/schema.inc):

  protected function createTableSql($name, $table) {
    $sql_fields = array();
    foreach ($table['fields'] as $field_name => $field) {
      $sql_fields[] = $this->createFieldSql($name, $field_name, $this->processField($field));
    }

    // If the table has no primary key, create one for us.
    // TODO: only necessary on Azure.
    if (isset($table['primary key']) && is_array($table['primary key'])) {
      $primary_key = array();
      foreach ($table['primary key'] as $key) {
        if (is_array($key)) {
          $primary_key[] = $key[0];
        }
        else {
          $primary_key[] = $key;
        }
      }
      $sql_fields[] = 'CONSTRAINT {' . $name . '}_pkey PRIMARY KEY CLUSTERED (' . implode(', ', $this->connection->quoteIdentifiers($primary_key)) . ')';
    }
    else {