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This fixes [--interpret-show-cst], which was inadvertently broken and
did not work at all (assertion failure).

This allows using --interpret together with --strategy legacy
and --strategy simplified, as one wishes.

LRijkstraFast: ignore transitions that became unreachable

Closes #64

See merge request !29

This fixes issue 64:
  Fatal error: exception File "src/LRijkstraFast.ml", line 892,
  characters 10-16: Assertion failed

After conflict resolution, a goto transition can become impossible to reach
(it still exists in the automaton but all reductions that allowed to
each it where removed).

In this case, LRijkstraFast does not even keep the unreachable class in
the corresponding partition. Previously it would error in this case, now
it just ignore the transition.

Here is a minimal grammar to reproduce the issue:
```
%token IDENT EOF
%start<unit> prog
%%
prog: decl* EOF { () }
decl: term { () }
term:
| IDENT { () }
| term term { () }
```

Use coq_makefile instead of custom Makefile. This should fix #60.