Allow limiting of RDS instances by specifying instance_identifiers in the config.
remove check for valid AWS credentials
Allow AWS authentication settings to be set via IAM Roles and Instance Profiles

Updated config template to show new configuration options
Merge pull request #40 from newrelic-platform/nathan/iam_roles

Nathan/iam roles
Ruby 1.8.7 bugfix
Merge pull request #41 from newrelic-platform/nathan/bugfix

Ruby 1.8.7 bugfix
Merge remote-tracking branch 'upstream/master'