Damage from fire blocks is calculated as if the fire was a full block

The Bug:

Relates to MC-150455.

Whether or not you are affected by fire is always calculated as if the fire were a full block. This means that fire on the side or bottom of a block can damage the player further away than its hitbox.

Steps to Reproduce:

1. Place any flammable block, for example an oak log.
2. Set fire to the side of the block using a flint and steel.
3. Put yourself into survival mode and walk into the block.
4. Walk slowly away from it.
   It will still set you on fire and damage you in even though it does not look like you are touching it.