* Add global status variables which tell you the progress of inplace alter table and row log buffer usage
  - (x 100%, it's 4-digit. 10000 means 100.00%)
  - Innodb_onlineddl_rowlog_rows
    Shows how many rows are stored in row log buffer.
  - Innodb_onlineddl_rowlog_pct_used
    Shows row log buffer usage in percent ( *100%, it's 4-digit. 10000 means 100.00% ).
  - Innodb_onlineddl_pct_progress
    Shows the progress of inplace alter table. It might be not so accurate becuase inplace alter is highly depend on disk and buffer pool status.
    But still it is useful and better than nothing.

* Add some log for inplace alter table
  - XtraDB will print some message before and after doing some task.