Fix NameError in stochastic_volatility.ipynb

When this notebook was added back in 85a017b (after being deleted in
138e145), a few names did not get updated to reflect the change of
`from pymc import *` to `import pymc as pm`.
Merge pull request #463 from kyleam/fix-stochastic_volatility-nameerror

Fix NameError in stochastic_volatility.ipynb
Show progress bar with parallel sampling

This commit enables a progress bar when using `psample`. This done by
using a progress bar for the first job. Although the information is for
only a single job, the progress of other jobs should usually be very
similar (and it is better than having no feedback on the state of the
sampler).

This closes #374.
Fix for r-hat calculation on multidimensional nodes
Merge pull request #462 from kyleam/mp-progressbar

Show progress bar with parallel sampling
Updated buildosx
Added comments to describe error handling in calc_rhat
Merge branch 'rhat_fix'