get: support single file/directory renames

e.g. scpclient.get('/etc/fstab',  local_path='ec2-fstab')
e.g. scpclient.get('/etc/zsh',  local_path='ec2-zsh-dir')

The above examples will only work provided local_path != cwd and
local_path is not an existing directory.
Merge pull request #18 from jtriley/feature-single-file-dir-renames

get: support single file/directory renames