1) Off-by-one in block allocation when block size != 1 KB
Due to a quirk in the on-disk layout of ext2, file systems with a block
size of 1 KB have block #1 as their first block, while all others start
on block #0.
2) We had no fallback mechanism when the preferred group was full
We now allocate blocks from the preferred block group as long as it's
possible, and fall back to a simple scan through all groups when the
preferred one is full.
bff59eff4b