Use char(32) for checksums instead of bigint unsigned

[koleo]

Starting from Percona Toolkit 3.0.11, the checksum function has been updated to use char(32) datatype in the checksum field, against bigint unsigned actually.

Other Pull Requests (#201) submitted the same change, but in an incomplete way and with errors.

This one has been tested and is valid (to the extent of my tests).

[boxcla]

Verified that @koleo has signed the CLA. Thanks for the pull request!

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

Nicolas Payart seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}