Update R-bnlearn to version 3.3.  Major changes:

  * fixed cpdag() and cextend(), which returned an error about
     the input graph being cyclic when it included the CPDAG of
     a shielded collider (thanks Jean-Baptiste Denis).
  * do not generate observations from redundant variables (those
     not in the upper closure of event and evidence) in cpdag()
     and cpquery().
  * added Pena's relevant() nodes identification.
  * make custom.fit() robust against floating point errors
     (thanks Jean-Baptiste Denis).
  * check v-structures do not introduce directed cycles in the
     graph when applying them (thanks Jean-Baptiste Denis).
  * fixed a buffer overflow in cextend() (thanks Jean-Baptiste
     Denis).
  * added a "strict" argument to cextend().
  * removed Depends on the graph package, which is in Suggests
     once more.
  * prefer the parallel package to snow, if it is available.
  * replace NaNs in bn.fit objects with uniform conditional
     probabilities when calling as.grain(), with a warning
     instead of an error.
  * remove reserved characters from levels in write.{dsc,bif,net}().
  * fix the Gaussian mutual information test (thanks Alex Lenkoski).