That's one that I've been mulling over in my mind and not understanding, so I'll throw it out to all of the experts here:
The Catholic church (not sure about protestant) really has a problem with suicide, it's one of those big sins. BUT, Jesus essentially knew about all of the events that led up to his arrest and crucifixion. So, he could have stopped these events at any time to avoid his death. Similarly, he could have used his miraculous cosmic powers at any time to get himself off of the cross.
Given all of that, didn't Christ commit suicide if he could have prevented his own death?