Use rack.input's read or string when appropriate.
Use rack.input's read or string when appropriate.

The rack spec support's read instead of string, causing errors with 
application servers like Phusion Passenger and NGINX.

References:  
*  http://rack.rubyforge.org/doc/SPEC.html
*  https://groups.google.com/forum/?fromgroups=#!topic/phusion-passenger/EYbAUYoh5qE
*  https://github.com/apotonick/roar-rails/issues/18
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