This is a cherry-pick of a4625acb with minor conflict
resolution.
Conflicts:
src/Makefile.am
=====
leveldb: integrate leveldb into our buildsystem
leveldb's buildsystem causes us a few problems:
- breaks out-of-tree builds
- forces flags used for some tools
- limits cross builds
Rather than continuing to add wrappers around it, simply integrate it into our
build.
