XSB Src (SVN)-old

Fix a strange bug (strange to me, and maybe only in MSVC) in accessing sched_heap in complstack resizing.

A tiny bit of refactoring and comment.

Cleaned up and updated some documentation, particularly w. dynamic loading.

Changed the names of variables from Dir to AZ, as Dir is ambiguous between Direction and Directory.

Fixed clang compiler error with filenanoseconds.

Fixed memory error when trying to access compl frame to reset level_num when there is no frame.

Moved num_sched and friends from schedrev_xsb_i.h where they were defined inside a function (emuloop) to emuloop.c where they were defined globally. This means that they can be used when expanding the compstack.

moving definitions of globals outside of a function.

two new preds:

machine:epoch_nanoseconds(Secs,Nanosecs)

This one actually works in windows, but windoze resolution is 100ns, while linux mac is 1 ns. This is a windoze limitation for some reason.

file_io:file_time_ns(file,secs,nanosecs)

This one only works in linux and mac. In windows, nanosecs=0.

If somebody has the patience to figure the windoze way for getting nanosecs here, it'd be great.

I tried but could not get the full picture and gave up.

There is this thing: https://docs.microsoft.com/en-us/windows/win32/sysinfo/retrieving-the-last-write-time

but unclear how to get from there to sec/nsec since epoch (1970). For some reason, some funcs in windows use 1601 as epoch and some 1970.

Fix bug in removing least element from sched heap; also fix bug in scheduling for incremental table maintence where there was a missing add-to-shced-heap.