py3: replace str.format(x) with `str % x` in githelp

githelp: drop the trailing period from single sentence output for consistency There are several instances of multiple sentence output, which I left alone. That is already nonstandard style, so dropping the period doesn't seem like an improvement.

hgweb: wrap {entries}* of filelog with mappinglist They were lists of mappings.

hgweb: don't use dict(key=value) to build a mapping dict in filelog It wasn't Py3 compatible because mapping keys must be bytes.