Avoid Rake monkey patch for Rake < 0.9. Fix #187

Rake versions under 0.9.x doesn't implement `Rake::Application#display_error_message` so we cannot monkey patch it in order to send the report to our API.

https://github.com/ruby/rake/blob/rake-0.8.7/lib/rake.rb#L2066-L2087

I think the best is not support Rake versions under 0.9.x since monkey patch `Rake::Aplication#start_exception_handling` is not the best idea.

WIth this PR we warn the users to upgrade their Rake version >= 0.9.x and disable Rake monkey patch.

For versions >= 0.9.x it just works as usual.
Should this say "with unsupported rake version"?