Fix for rails3.1: DEPRECATION WARNING: class_inheritable_attribute is de...

[millisami]

Making it compatible with Rails 3.1 to suppress the following warnings that clogs the console log.

DEPRECATION WARNING: class_inheritable_attribute is deprecated, please use class_attribute method instead. Notice their behavior are slightly different, so refer to class_attribute documentation first. (called from emits_pfeeds at /var/lib/jenkins/jobs/CloudFactory/workspace/vendor/plugins/pfeed/lib/pfeed.rb:20)
DEPRECATION WARNING: class_inheritable_attribute is deprecated, please use class_attribute method instead. Notice their behavior are slightly different, so refer to class_attribute documentation first. (called from emits_pfeeds at /var/lib/jenkins/jobs/CloudFactory/workspace/vendor/plugins/pfeed/lib/pfeed.rb:20)
DEPRECATION WARNING: class_inheritable_attribute is deprecated, please use class_attribute method instead. Notice their behavior are slightly different, so refer to class_attribute documentation first. (called from emits_pfeeds at /var/lib/jenkins/jobs/CloudFactory/workspace/vendor/plugins/pfeed/lib/pfeed.rb:24)
DEPRECATION WARNING: class_inheritable_attribute is deprecated, please use class_attribute method instead. Notice their behavior are slightly different, so refer to class_attribute documentation first. (called from emits_pfeeds at /var/lib/jenkins/jobs/CloudFactory/workspace/vendor/plugins/pfeed/lib/pfeed.rb:24)
DEPRECATION WARNING: class_inheritable_attribute is deprecated, please use class_attribute method instead. Notice their behavior are slightly different, so refer to class_attribute documentation first. (called from receives_pfeed at /var/lib/jenkins/jobs/CloudFactory/workspace/vendor/plugins/pfeed/lib/pfeed.rb:69)