[Developers] MCMC not working in ADMB10

[dave fournier]

What needs to be done is to declare a random_number_generator object at 
a higher level
such as in xxmcmc.cpp and then use its member function better_rand to 
generate the
random number.  this means that the random number generator object will 
need to
be passed to the function bounded_multivariate_normal  the way it is 
done now
you are creating a new random_number_generator object in each call to 
better_rand.
also the random_number_generator class has no destructor to clean it up 
so this
is causing a huge memory leak as well as being very inefficient.