Remove spurious = DIR from examples, test
Include tracking of fixed parameters, since that is needed for acceptance/
rejection.

* Parameter states (FIXED, ACIGNORE) kept track of as bitwise flags.
* Fixed parameters not counted in z^(nparams-1) part of acceptance rule.
* Fixed parameters kept at old value when generating new step in chains.
* Amount to sleep for while waiting for message set in mcmc_affine namespace.
  Default value lowered to 1 usec, much more approriate for the example scripts.
* Changed example programs to be able to return help text if not invoked vi
  mpirun.
Parameters are now stored as float, likelihoods as double.

Generally, the parameters should not need 64 bit precision.
The idea is to save some space.  However, since likelihoods may
have large additive constants (since normalization is hard),
those are kept as double.
Add ability to do fixed number of burn-in steps rather than
 messing about with the autocorrelation.