Support old/new versions of boto

boto made a mess with the get_all_instances() etc. methods, and we must
support both "old" and "new" boto versions. In particular, we support:

 - boto 2.34.1 ("new" boto, shipped with RHEL 6)
 - boto 2.2.2  ("old" boto, shipped with Ubuntu 12.04 LTS)
Added debug messages for old boto versions
Do not echo PID and status twice when stopping
Merge branch 'feature-oldnewboto'

Fixes #8