Fixed RSpec deprecation warning
Fixed rpc method detection code

Old code used `try` method which doesn't exist if you don't use
ActiveSupport.
Added unit tests for logging code
Improve logger behaviour

Old `set_logger` used to override Rake's `env`, even if requested path
didn't match thrift endpoint.

Also improved error reporting to include actual error text and stack
trace.
Refactor unit tests

Moved some boilerplate into RSpec `let`, grouped some tests in context.
Merge pull request #2 from frantic/fix-rspec

Fix RSpec tests & logger