hamfisted addition of command-line option to add support for
backing up just a single org, instead of all orgs. intended
to simplify ec server migration scenarios where there may be
many orgs present but not involved in the current migration
effort.

skips backing up users and user_acls on the assumption that
they will already have been restored to the destination server.
Update ec_backup.rb

incorporating suggested changes
Merge pull request #31 from strickra/master

add support for backing up just a single org