DibiMsSql2005Driver: default charset set to UTF-8

If charset is not specified in config, NULL is passed as connection option and 'Invalid value type for option CharacterSet was specified.  String type was expected.' is thrown.
DibiPdoDriver: applyLimit() for sqlsrv driver

Added table alias has been tested with MS SQL Server 2012 directly and over ODBC.
DibiPdoDriver: added identifier escaping for sqlsrv
DibiMsSql2005Driver: fixed identifier escaping

Annoted link to MS SQL doc does not talk about open bracket '[' escaping, only closing bracket ']'.

dibi::query('CREATE TABLE %n (id INT)', 'abc[]def');
 - old: creates table 'abc[[]def'
 - new: creates table 'abc[]def'
Merge pull request #83 from milo/sqlsrv-fixes

Sqlsrv fixes