More mysqldump commands.

I also modified the previous commands so passwords don't show in the
history.
Merge branch 'master' of https://github.com/codehill/cheat into codehill-master

* 'master' of https://github.com/codehill/cheat:
  More mysqldump commands.
Trivial changes to the mysqldump cheatsheet.
Fixed a typo I introduced to the mysqldump cheatsheet.