Allow realloc() with allocators

[sofian]

However, the StaticAllocator would return an error if we are trying to reallocate new space while the pointer is already ahead. And possibly return a warning if we are trying to reallocate less space in the same situation.

The idea is that we are using the fact that in many cases we will make the calls sequentially (ie. adding one element right after another).

This is yet just an idea. But it's easy to implement.