Ask etags to stop language auto-detection from falling back to Fortran and C?

[Dmitry Gutov]

So, I want auto-detection, but the list of files I'm passing to etags is 
very naively auto-generated (basically, all files in the project), and 
includes languages that etags doesn't know about (e.g. CSS).

How do I stop it from parsing them as Fortran files? Please add an option.