Update Graphs.m2

This is the all new Graphs package.
Update GraphicalModels.m2

Modified trekSeparation to stop monkeying around *inside* a Digraph.  Fixed a type in the example of directedEdgesMatrix documentation.
Update Posets.m2

Lots of small changes.
Update Graphs.m2

Modified addEdges to not break NautyGraphs.
Update Graphs.m2

Adjust for the vertices symbol in SimplicialComplexes.
Minor changes to Divisor.m2
Merge remote-tracking branch 'upstream/pull/160'
fix an internal error handler

so in addition to printing a message it aborts the program
undo a change we did to the 4ti2 configure script
Defended against calling minimal primes on the unit ideal
Merge remote-tracking branch 'upstream/pull/161'
Update GraphicalModels.m2
Update Graphs.m2
Update Nauty.m2
Update NautyGraphs.m2
Update Posets.m2
Update SimplicialDecomposability.m2
convert an unseen warning message to a call to "abort"
Update Graphs.m2
Update GraphicalModels.m2