* implement el_get(EditLine *, int op, void *result), which does the
inverse of el_set()
* add EL_EDITMODE operation to el_set and el_get; if non zero editing
is enabled (the default).
* add "edit on | off" editrc command, which modifies EL_EDITMODE.
users can now add '*:edit off' in ~/.editrc as an advisory to
disable editing.
NOTE: at this time EL_EDITMODE is just an indication of the
state of the 'edit' command. It's up to the application to check
this after el_source() or el_parse() to determine if editing is still
required.
line (a la ^R). This is useful if the binding outputs information and
mucks up the input line. To be used in ``list-choices'' bindings (refer
to the ^D binding in csh when filec is set)
