Changes since 20181221 are mostly portability related
hence the large gap in versions imported.
There are however some bug fixes, and a rework of filemon handling.
In NetBSD make/filemon/filemon_ktrace.c allows use of fktrace
and elimination of filemon(4) which has not had the TLC it needs.
FreeBSD filemon(4) is in much better shape, so bmake/filemon/filemon_dev.c
allows use of that, with a bit less overhead than the ktrace model.
Summary of changes from ChangeLog
o str.c: empty string does not match % pattern
plus unit-test changes
o var.c: import handling of old sysV style modifier using '%'
o str.c: refactor brk_string
o meta.c: meta_oodate, CHECK_VALID_META is too aggressive for CMD
a blank command is perfectly valid.
o meta.c: meta_oodate, check for corrupted meta file
earlier and more often.
* meta.c: meta_compat_parent check for USE_FILEMON
patch from Soeren Tempel
o meta.c: fix compat mode, need to call meta_job_output()
o job.c: extra fds for meta mode not needed if using filemon_dev
o meta.c: avoid passing NULL to filemon_*() when meta_needed()
returns FALSE.
o filemon/filemon_{dev,ktrace}.c: allow selection of
filemon implementation. filemon_dev.c uses the kernel module
while filemon_ktrace.c leverages the fktrace api available in
NetBSD. filemon_ktrace.c can hopefully form the basis for
adding support for other tracing mechanisms such as strace on
Linux.
o meta.c: when target is out-of-date per normal make rules
record value of .OODATE in meta file.
o parse.c: don't pass NULL to realpath(3)
some versions cannot handle it.
o parse.c: ParseDoDependency: free paths rather than assert
plus more unit-tests
