Reverse linked list order

[jfrimmel]

Currently the linked list of blocks is always extended in a way, that new blocks are appended on the far end of the chain. This is bad for short-lived allocations, which need 1. to traverse the whole chain to find a free block to allocate, then performing the work and then 2. traversing the whole list again in order to find the block "just" allocated. Since those allocations typically are stack-like (LIFO), it would make sense to reverse the order in which blocks are chained in the list: new blocks should come first.