use macros to set/read options

use macros to set/read options
rename functions/fields to POSIX names
make comments consistently use capital letters
get rid of global variable stream and pass around current stream pointer
don't cast free to void
add FTS__NOINSTR flag, instead of using 0 as "no user instructions"
allow fts_children call for FTS_{D,DNR,DNX} instead of just FTS_D
change fts_build so that fts_children can read FTS_DNX directories
make fts_stat return FTS_NS on stat failure, not FTS_ERR
make fts_stat unset errno on FTS_{NS,SLNONE} conditions

SCCS-vsn: lib/libc/gen/fts.c 5.11