(ef_byname_from): New.

(ef_byname_from): New.
(set, mission, multifire, fuel, cons_choose, cede): Use it instead of
ef_byname().  Remove the hacks to map unwanted results to wanted
results.  The hacks in set() were broken: bad input made the code cast
arbitrary items to union trdgenstr, with potentially disastrous
consequences.  Closes #906483 and #906486.

(set): Less cryptic prompt and diagnostics.