1. Error handling is introduced. Now TSQLServer/TSQLStatement returns error code - GetErrorCode()
   and message - GetErrorMsg() of last operation.
   If desired, error output can be suppressed for TSQLServer. Correspondent changes done in implementation
   for Oracle, MySQL, ODBC
2. New methods of TSQLServer class for transactions control: StartTransaction() / Commit() / Rollback().
   As desfault implmenetaion in TSQLServer class they corresopnd to SQL "START TRANSACTION", "COMMIT", "ROLLBACK" queries.
   For Oracle, MySQL and ODBC specific implmentaion were done while there special methods should be called.
3. Some other new methods of TSQLServer class:
     IsSupportStatement() - return kTRUE if plugin has TSQLStatement implementation
     GetMaxIdentifierLength() - return maximum allowed length of identifiers
4. Bugfix in TODBCRow class


git-svn-id: http://root.cern.ch/svn/root/trunk@15124 27541ba8-7e3a-0410-8455-c3a389f83636