On 1.8.8 entitydata @e[type=WitherBoss] {Invul:550} this comand make the wither boss a friendly mob who only atack other mobs and move around you in peace. On snapshots I found the WitherBoss with this comand has NoAI. :s I will miss my friendly wither boss.
RIP FRIENDLY WITHER BOSS
RIP AGRO GIANT
RIP MOBS MOVING UNDER WATER AND LAVA
WAI. See MC-57569