help: fix help -c/help -e/help -k
Before, hg help -c was the same as hg help, now it only shows commands.
Before, hg help -e was the same as hg help, now it only shows extensions.
Before, hg help -k crashed, now it shows all topics.
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.