1963 eunit bigcouch

This brings in the relevant tests for `couchdb-couch` from https://github.com/apache/couchdb/pull/253 and updates them to work with the BigCouch merge. The actual running of eunit tests will be added later in another PR to the `couchdb` repo.

There are three items in particular I would like feedback on before this PR gets merged. I've added a `test_util` module that includes functions for starting/stopping CouchDB and similarly starting/stopping the `config` application. It would be great to get some feedback on whether the approach taken for starting those applications could be improved upon. The relevant commits are 66ee5e3 and 634c475.

I also added the `test_util` module into the `src` dir of `couchdb-couch` so that it's readily available to all the other test suites that need a running CouchDB for testing, but there could be a better approach there.

The other question I have is on getting absolute paths for eunit. Currently I'm using an environment variable passed from make to get access to the build dir in `couch_eunit.hrl`. This is a bit of a hack, so alternative suggestions are welcome. Also along these lines, I need to rework the paths in the `?CONFIG_CHAIN` macro of `couch_eunit.hrl` to match whatever paths we end up using for the generated eunit ini files.

There are a number of problematic tests that I've disabled for the time being in 0efdc71. I think it's better to get a running test suite in place and come back to those tests individually when we can.