[Dbix-class] wishlist: "might_have_many"

[Mark Hedges]

I found that if I do a prefetch on a Foo RS to its have_many 
Bar, but it doesn't have any Bars, I don't get the Foo at all.

This is similar to a problem where if I do a prefetch from one 
to another with a 1:1 relationship, but the other doesn't exist, 
it does not work if I defined with has_one but it does work if I 
defined if might_have.

However there isn't a fix for a 1:N relationship.  (Doesn't 1:N 
imply that N could equal 0?)  Instead I have to remember where 
this drop might occur and I get no object, and I can't prefetch.

Mark