Attached is a revised patch that should address the comments raised:

* The new minor mode is now disabled by default.

* The patch doesn't affect .dir-locals.el.

* The new minor mode is now (less ambitiously) called Electric Quote mode, not 
Electric Punct mode.

* Electric Quote mode combines well with Electric Pair mode's pairings of ` and 
', turning them into electric ‘ and ’.  I did not implement the electric quote 
pairing of “ and ”, as it would be trickier to add and anyway any such pairing 
is considerably lower priority for Elisp.

Plus another issue I found while testing:

* Electric quoting is now inactive in buffers whose coding systems can't 
represent curved quotes.