Ken Manheimer <ken.manheimer@gmail.com> writes:
> i now have a fix i'm more confident about, because (1) it takes care
> of another problem i noticed, even with my previous fix, and (2) it
> departs less from the checked-in version of the function, leaving less
> room for betrayal of unfamiliar concerns.

I propose the following change instead, which, in addition to
incorporating your fix, restores the useful special handling of field
boundaries.  As noted in another thread, C-a and C-e behaviour is
currently broken in the minibuffer, in *shell* buffers, in entry
fields in customization buffers, and all other places where fields are
used.  This makes `move-{beginning,end}-of-line' inconsistent with the
original `{beginning,end}-of-line' commands (which are still
available) and the underlying `line-{beginning,end}-position'
functions.

Meanwhile, I committed two (hopefully non-controversial) related fixes
in CVS; the first is for an annoying cursor display problem when point
is just before an ellipsis coming from an invisible overlay.  The
second fixed `constrain-to-field' to always return the right result
when new-pos or old-pos is on a field boundary.