Fix bug when a bad help topic is passed, and add tests.

e.g. 'help ZZZ'

Also, rename a spec test file so we can put all bash-specific builtins
in it.

Fixes issue #51.

core/builtin.py

@@ -864,8 +864,8 @@ def Help(argv, loader):
  else:
    try:
      section_id = osh_help.TOPIC_LOOKUP[topic]
    except IndexError:
      util.error('No help for topic %r', topic)
    except KeyError:
      util.error('No help topics match %r', topic)
      return 1
    else:
      try:

spec/builtin-type.test.sh → spec/builtin-bash.test.sh

@@ -25,3 +25,15 @@ type -t find xargs
type -t echo ZZZ find =
echo status=$?
# stdout-json: "builtin\nfile\nstatus=1\n"

### help
help
help help
# status: 0

### bad help topic
help ZZZ 2>$TMP/err.txt
echo "help=$?"
cat $TMP/err.txt | grep -i 'no help topics' >/dev/null
echo "grep=$?"
# stdout-json: "help=1\ngrep=0\n"

test/spec.sh

@@ -271,9 +271,10 @@ builtin-test() {
    ${REF_SHELLS[@]} $OSH "$@"
}

# Bash impleement type -t, but no other shell does.  For Nix.
builtin-type() {
  sh-spec spec/builtin-type.test.sh \
# Bash implements type -t, but no other shell does.  For Nix.
# zsh/mksh/dash don't have the 'help' builtin.
builtin-bash() {
  sh-spec spec/builtin-bash.test.sh \
    $BASH $OSH "$@"
}