Save YAML with problems found during checksumming

Make possible to have an easily parseable structure to find skipped tables, tables that couldn't be checksummed and other unexpected events (can't think of one right now) that could lead to undetected inconsistencies in the slaves. This allows for automation of checksumming (errors in the process could be checked using programmatic means, instead of parsing output), and would be helpful for very large checksums where going through the output is rather tedious (--replicate-check could use it to ouput summary of issues along with summary of found inconsitencies)