histedit: renaming parts to which _histedit was split
I recently broke _histedit into multiple functions, each of which
had 'action' in its name. This is a little bit confusing since 'action'
is the word for an individual histedit plan item (such as edit or pick).
To avoid this confusion, these functions are now renamed to contain
'histedit' as part of their names.
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.