Add test for catching sampler issues on a simple, bounded model

[syclik]

Summary:

@betanalpha fixed #1972. We should add a test so it doesn't recur.
(Thanks, @YannickJadoul)

Description:

This model did not sample correctly in v2.10:

parameters {
   real<lower = 0, upper = 1> theta;
}
model { 
}

We should check that the distribution of the samples is uniform from 0 to 1.

Additional Information:

This has been fixed on the current release. We want to add a test that will pass on the current release and fail on v2.10.0.

Current Version:

v2.11.0