What version of Review Bot are you using?
1.0.1, with Reviewboard 3.0.18

Which tool(s) does this relate to?
flake8, or any tool

Describe the enhancement and the motivation for it.
Our repo uses multiple languages, such as Python and Java. If I enable flake8, reviewboard will always call the flake8 bot even if I only change Java code. This causes extra noise and confusion in a code review.
Given flake8 already has a handle_file() function, it would be nice if Reviewboard somehow called that routine for all patched files before deciding to run the bot itself.  
Please provide any additional information below.