subjects-sameday.c tablix2 port

Hi all!

I have been looking at the new kernel (the docs are great!) and i have
ported one of my old modules just to give it a try.
It seems to work OK, although i have not written test-cases. I have not
delved much into the code yet, so maybe it can be rewritten to be
faster.

I am going to do some tests with my timetables and tablix2, and i will
come back here to tell what i find out.

Regards,
Antonio.