Pervasive change of BipartiteGraph implementation

Pervasive change of BipartiteGraph implementation

- Added conditional compilation of inference methods
- New implementation of BipartiteGraph: it does not store the
node properties anymore, and nor does it store an adjacency
matrix. Instead, it stores lists of neighbors. An easy way
of iterating over neighbors is to use boost::foreach.
- Interface changes in FactorGraph:
  * delta(const Var &) -> delta(size_t)
  * Delta(const Var &) -> Delta(size_t)
  * makeCavity(const Var &) -> makeCavity(size_t)
  * removed MakeFactorCavity(size_t)
  * removed ExactMarginal(const VarSet &)
  * removed ExactlogZ()
  * removed isConnected() (moved to BipartiteGraph)
  * vars() -> vars
  * factors() -> factors
- Interface changes in RegionGraph:
  * nr_ORs() -> nrORs()
  * nr_IRs() -> nrIRs()
  * ORs() -> ORs
  * IRs() -> IRs
- Fixed typo in utils/fg2dot.cpp