Fix multiple problems with the getconf builtin (#280)

This commit fixes three problems with getconf pathbound builtin:
1. The -l/--lowercase option did not change all variable names to
   lower case.
2. The -q/--quote option now quotes all string values. Previously,
   it only quoted string values that had a space or other
   non-shellsafe character.
3. The -c/--call, -n/--name and -s/--standard options matched all
   variable names provided by 'getconf -a', even if none were
   actual matches.

Additionally, references to the confstr and sysconf functions have
been updated to reference section 3 of the man pages instead of
section 2.

src/lib/libast/port/astconf.c:
- Previously, only values that had spaces in them were quoted. Change
  that behavior to quote all string values by using the FMT_ALWAYS
  flag. Bug report: https://github.com/att/ast/issues/1173
- Not all variable names were printed in lowercase by 'getconf -l'.
  Fix it by adding a few missing instances of fmtlower.
  Bug report: https://github.com/att/ast/issues/1171
- Add the missing code to the '#if _pth_getconf_a' block to handle
  -c/-n/-s while parsing the OS's native 'getconf -a' output. This
  approach reuses code for name matching from other parts of
  astconflist(). Resolves: https://github.com/ksh93/ksh/issues/279

src/lib/libcmd/getconf.c:
- Update the documentation to note the -q flag only quotes strings.

src/cmd/ksh93/tests/bulitins.sh:
- Add regression tests for the getconf bugs fixed in this commit.

Co-authored-by: Martijn Dekker <martijn@inlv.org>

src/lib/libast/comp/conf.sh

@@ -367,7 +367,7 @@ IFS=$ifs; set +f
 export CONF_getconf CONF_getconf_a
 
 case $verbose in
-1)	echo "$command: check ${CONF_getconf:+$CONF_getconf(1),}confstr(2),pathconf(2),sysconf(2),sysinfo(2) configuration names" >&2 ;;
+1)	echo "$command: check ${CONF_getconf:+$CONF_getconf(1),}confstr(3),pathconf(2),sysconf(3),sysinfo(2) configuration names" >&2 ;;
 esac
 {
 	echo "#include <unistd.h>$systeminfo