[Q] Change forms like (delq nil (mapcar ...)) to (mapcan ...).

[Stephen J. Turnbull]

QUERY

Aidan Kehoe writes:

 > Replace the O2N (delq nil (mapcar (lambda (W) (and X Y)) Z)) with
 > the ON (mapcan (lambda (W) (and X (list Y))) Z) in these files.

This can't work as written, can it?  If X is nil, if Y is nil, it will
wrap nil in a list and the nil will not be deleted.  I guess from a
quick look at the patch that it's expected that if X is non-nil, Y
will be non-nil, but are you sure?

I'm also not convinced that this is necessarily faster if (length Z)
is small, as the mapcan version involves extra consing.