Better handling of attributions in DoChangelogs

Stray "<" and ">" that are not part of the email address are not permitted in fast-import streams and would make them invalid, but bailing out is too extreme. Instead, we can remove those spurious characters to make the attribution valid.

Additionally, some of those "<" and ">" might come from legit parenthesis in the name, that a previous massaging converted to angle brackets to cater for old-style attributions where round brackets delimited emails. In front of the actual email block where angle brackets should remain, replace the brackets by round ones.