Add raw tree buffer info to "struct tree"

Add raw tree buffer info to "struct tree"

This allows us to avoid allocating information for names etc, because
we can just use the information from the tree buffer directly.

We still keep the old "tree_entry_list" in struct tree as well, so old
users aren't affected, apart from the fact that the allocations are
different (if you free a tree entry, you should no longer free the name
allocation for it, since it's allocated as part of "tree->buffer")

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>