Hello all!

Thank you for your helpful comments and ideas!

I've committed an improved version of the pagination. As you advised I chose and implemented (2) variant. I alter sorting order in SQL query depending on the type of the current page border. So, now all operators (gotofirst, gotolast, next and previous) are working.

Also, I added pagination for builds page ("eval" query). Here I face a problem that Denny mentioned before. 

The tuple of data cells should uniquely identify one row in the result.  (If it
didn't, you'd skip the other same-value rows when going to the next page)

I order builds by stoptime and there are some builds with identical stoptime timestamps. I am not sure what is the best way to support pagination filtering by multiple columns. Do you have ideas on how to implement tuple comparison and other routines in SQL and guile in a convenient and flexible way?   

Could you please review the last 3 commits and maybe find some more issues besides that?

Best regards,

Tatiana