Multi-way conflicts cause Graham to crash

[jack-pappas]

Graham is currently unable to handle multi-way conflicts at all -- they cause the library to crash when attempting to compile an LR(0) (incl. SLR(1), LALR(1)) table.

In the short-term, this could be fixed by using the same conflict-resolution algorithm fsyacc uses. It causes issues of it's own, but it'll keep the library from crashing and may be useful for getting fsharpyacc to parity with fsyacc.

For the long-term, we'll need to implement a robust algorithm for multi-way conflict resolution.