Db command improvements and new features with tests

This PR contains three changes/features with its tests.

1. `db:maintain:check-tables` has been refactored to run properly on InnoDB tables.
2. Added command db:variables to show server variables
3. Added command db:status to show the current server status.

I left some todos in the code which are pretty time consuming but can be solved e.g. on the hackathon.

I've merged n98-magerun/develop branch into this branch to be update to date with changes or maybe if there are breaking changes for my code.

If there should be something weird (code, naming, etc) please comment :-)

Otherwise please merge :-) Thanks!

The following printscreens shows the commands more clearly.

![screen shot 2014-11-03 at 4 08 47 pm](https://cloud.githubusercontent.com/assets/372027/4878900/475e5ff4-631c-11e4-8b1d-6772685bfacf.png)
![screen shot 2014-11-03 at 4 37 30 pm](https://cloud.githubusercontent.com/assets/372027/4878902/475f7c18-631c-11e4-8197-c0f8c722eb05.png)
![screen shot 2014-11-03 at 4 37 48 pm](https://cloud.githubusercontent.com/assets/372027/4878899/475cac9a-631c-11e4-8ad8-790f6f2fe527.png)
![screen shot 2014-11-03 at 4 38 17 pm](https://cloud.githubusercontent.com/assets/372027/4878903/4761688e-631c-11e4-9cd8-b7f851294ef8.png)
![screen shot 2014-11-03 at 4 38 34 pm](https://cloud.githubusercontent.com/assets/372027/4878901/475eee4c-631c-11e4-9b4a-57ae9018a8af.png)
![screen shot 2014-11-03 at 4 38 50 pm](https://cloud.githubusercontent.com/assets/372027/4878904/4764ce52-631c-11e4-9d49-08e0c37be332.png)
![screen shot 2014-11-03 at 4 39 56 pm](https://cloud.githubusercontent.com/assets/372027/4878905/478534da-631c-11e4-8fc2-9d95a88b621f.png)