nullable and resize

[olafvdspek@…]

Please notice that nullable has no effect on the containers interface (except for is_null() functions).

It doesn't apear to affect the is_null() functions either.

ptr_vector::resize

Doesn't initialize elements if it enlarges the container. Doesn't appear to be efficient, as it adds one element at a time.

[olafvdspek]

My bad, turns out resize() allocates new elements, even if the container allows null values. This is unexpected behaviour and is poorly documented.