Support Drush 7

The civicrm drush command to install civicrm is not compatible with drush v7 (current mastet)

The function _drush_sql_get_db_spec(); is removed in drush 7.

Possible patch approach could be

• $db_spec = _drush_sql_get_db_spec();
  + if (version_compare(DRUSH_VERSION, 7, '>=')) { + $sql = drush_sql_get_class(); + $db_spec = $sql->db_spec(); + }

  + else

  { + $db_spec = _drush_sql_get_db_spec(); + }

  +