Minor futzing with the LevelDB copyright checks, add a WiredTiger
copyright notice to the leveldb/port/ files (such as they are).

Move src/api/api_XXX into src/conn/XXX, there's no reason to have an api
directory in the lower level (and it's about 100 lines of code, anyway).
Put the LevelDB API into the public domain, add a copyright notice to
leveldb_wt.h, it's simpler that way.
Add LevelDB/Google Inc. to the list of 3rd party software that may
be part of a WiredTiger library build.
Merge pull request #1084 from wiredtiger/leveldb-copyright

LevelDB copyright