Fix the Sinatra tests to more closely resemble production settings

This commit makes 3 changes to the Sinatra application that more
closely resembles what someone would use in production (if throughput
is a concern) and should improve performance on both JRuby and Ruby.

* We disable Sinatra's static file serving so it doesn't waste time on
each request looking for static files, since we have none. In
production this is usually handled by a frontend server anyway.

* We specify which JSON encoder to use so that sinatra/json doesn't
try several options on each request until it finds one it can use.

* We disable the per-request connection pooling in
sinatra/activerecord and instead use ActiveRecord's with_connection to
explicitly control connections. The default behavior is overly
simplistic and incurs expensive synchronized method calls on every
request, even if the request doesn't touch the database.

This change makes the non-database routes several times faster, and
should improve the performance of the database route a bit less.
Use the same version of Jackson for JSON tests

As discussed at https://groups.google.com/forum/#!topic/framework-benchmarks/WM9k_hwkhLQ
PR #640 Remove newly added jetty-maven-plugin.

Its purpose was to run the app as a smoke test to verify it is not broken.
But it doesn't work atm.
Make test apples to apples with other framework tests that have started caching the response buffer
Reuse the IResource instance.

The IResource is stateless so it is OK to reuse it.

Optimize imports
Minor optimizations to the way the /json response is created.

* reuse the IResource - it is stateless so it can be reused thread safely
* use Content-Length response header
No need to initialize IdentifierLoadAccess for each record
Optimize imports
Don't log WARN

As prescribed at http://www.techempower.com/benchmarks/#section=code do as less logging as possible
Merge branch 'master' into wicket-optimizations
verify Added some beginning tests for verification
verify Added in json validation attempt
verify Syntax problems.
verify Easier
verify Fixed more syntax errors
verify Do not benchmark if not json_url_passed
verify Added some constants
Make sure the id is between 1 and 10000
verify More verification implementation
verify Syntax errors