Add to Bayes function doc JAGS dependency

[egouldo]

Ensure that JAGS dependency for Bayesian functions is documented in the function man for the Bayes agg methods.

[egouldo]

Note that some users might have a problem when loading the rjags library if they installed jags using homebrew, macports or other installer and the install location is somewhere other than the default. Messages such as as the following may appear:

library(rjags)
Error : .onLoad failed in loadNamespace() for 'rjags', details:
  call: dyn.load(file, DLLpath = DLLpath, ...)
  error: unable to load shared object '/Users/casallas/Library/R/3.0/library/rjags/libs/rjags.so':
  dlopen(/Users/casallas/Library/R/3.0/library/rjags/libs/rjags.so, 10): Library not loaded: /usr/local/lib/libjags.3.dylib
  Referenced from: /Users/casallas/Library/R/3.0/library/rjags/libs/rjags.so
  Reason: image not found
Error: package or namespace load failed for ‘rjags’

One workaround is to install rjags from source:

install.packages("rjags",type = "source")