Sometimes it's useful to lookup a string without terminating it with a
zero. We can do that relying on ebmb_lookup() since the string in the
tree contains a zero.
We needed to upgrade ebtree to v5.0 to support string indexing,
and it was getting very painful to have it split across 2 dirs
and to have to patch it. Now we just have to copy the .c and .h
files to the right place.