clarify asc/desc maj/min bib sort logic
clarify asc/desc maj/min bib sort logic

That is, what does descending major sort imply for different types of
minor sorts? Now implemented as: bib_sort() takes separate asc_maj and
asc_min flags, and bib_sort.dir function maps major, minor, asc to two
booleans.

altaf-ali/dfr-browser,joncgoodwin/dfr-browser,joncgoodwin/dfr-browser,joncgoodwin/dfr-browser,altaf-ali/dfr-browser,altaf-ali/dfr-browser,agoldst/dfr-browser,agoldst/dfr-browser,altaf-ali/dfr-browser,joncgoodwin/dfr-browser,joncgoodwin/dfr-browser,agoldst/dfr-browser,agoldst/dfr-browser