Sqli error based added Firebird support

I did setup a Firebird sql db (http://www.firebirdsql.org/) locally with a vulnerable website in order to test Arachni and it failed, so here are the fixes (hope i did not mess something up)

ps: sorry for the big number of commits, wish i know how to squeeze them in a single commit and send it like that. 

![backbox x64-2013-08-20-00-51-12](https://f.cloud.github.com/assets/4062655/990215/ee997b60-0926-11e3-8e48-5bc91f213ea3.png)