Sqlite rollback

Implemented by Mario Barrera \<zat\>.
I tweaked it and fixed some things.
I also added support for showing multiple rollback actions(Up to 5 by default).

Results:
* /rollback_check with any options takes about a second on a rollback DB with 15403963 entries(2.1G in txt format).
* A SQLite rollback DB is approximately one third of the size of a rollback.txt containing the same entries(the aformentioned log becomes 691M in size).
* Running /rollback(_check) doesn't hog memory. :-)

Existing rollback.txt databases are automatically converted when the server starts.