Fix #140: make 'path' required for Connection.api_request.

After consideration, I don't believe there is any sensible default value for 'path'.

See #140.
Gotcher. Let's try to make a concerted effort to keep PR's scoped correctly (i.e. as stated).

To fix this, I have written up a bit of `bash`/`git` magic.

This assumes your remote is called `origin` and points to either the `http` or `ssh` clone URL (e.g. https://github.com/tseaver/gcloud-python/)
```sh
REMOTE_NAME="origin"
LOCAL_140_BRANCH="140-connection.api_request-handle_path_none"
REMOTE_140_BRANCH="140-connection.api_request-handle_path_none"
git checkout --detach HEAD
git branch -D $LOCAL_140_BRANCH
# Check out clean version of master.
git branch $LOCAL_140_BRANCH $REMOTE_NAME/master
# Track the desired branch you want to push to (instead of master).
git branch $LOCAL_140_BRANCH -u $REMOTE_NAME/$REMOTE_140_BRANCH
# Descend into the branch (from detached state).
git checkout $LOCAL_140_BRANCH
# Play back the desired commit.
git cherry-pick ccd8a5e1190d6dbaea2b55973d275f9b56979eda
# Do stuff to make sure it adds the commit smoothly.
# Do a force push to overwrite the previous history.
git push -f $REMOTE_NAME $LOCAL_140_BRANCH:$REMOTE_140_BRANCH
```