Replace b tags

[Ryan J Ollos]

There are several instances of b tags that should probably be replaced with strong tags.

The codebase was inspected after comment:12:ticket:6634:

$ grep -r tag.\b\(
sample-plugins/Timestamp.py:        return tag.b(format_datetime(t, '%c'))
trac/notification.py:                    "configuration.", from_=tag.b('[notification] smtp_from'),
trac/notification.py:                    reply_to=tag.b('[notification] smtp_replyto')))))
trac/timeline/web_ui.py:                  tag.b(exception_to_unicode(exc)), class_='message'),
trac/wiki/intertrac.py:                yield tag.tr(tag.td(tag.b(prefix)),
trac/wiki/intertrac.py:                             tag.td('Alias for ', tag.b(intertrac)))
trac/wiki/intertrac.py:                    yield tag.tr(tag.td(tag.a(tag.b(prefix),
trac/wiki/default-pages/WikiMacros:        return tag.b(format_datetime(t, '%c'))
trac/versioncontrol/web_ui/changeset.py:                [tag.li(tag.b(path) if isdir else path)