Added requirements file to install dependencies.
Removed scikits.sparse as it's not a hard dependency.
Merge pull request #228 from pymc-devs/jsalvatier

Removed stochastic vol dependence on scikits.sparse. Renamed track_progressbar -> progressbar.
Removed more optional dependencies.
Added tests to installation.
autopep8 codebase.
Merge pull request #232 from pymc-devs/pep8ify

autopep8 complete code base
Added discrete variable support for Metropolis and a BinaryMetropolis step function
Fixed bugs in BinaryMetropolis
Cleaned up discrete type support
Added discrete variable support for Metropolis and a BinaryMetropolis step function
Fixed bugs in BinaryMetropolis
Cleaned up discrete type support
Merge branch 'metropolis' of github.com:pymc-devs/pymc into metropolis

Conflicts:
	pymc/step_methods/metropolis.py
Added modes to discrete distributions to address #244
Added call to numpy.random.seed to sample so that psample does not produce identical traces
fixed metropolis related issues: stalling from having lambdas during parallel sampling and non convergence in tests
added better error when no default is found
exercise default values for distributions
fix argument errors