* src/parse-simulation.c: Replace reference counting with
parse_state_retain everywhere.
(free_parse_state): Make this function iterative instead of
recursive. Long parse_state chains were causing stack exhaustion.
* tests/counterexample.at: Fix expectations.
Fixes the SEGV in test 247 (counterexample.at:195): "S/R after first
token".
* src/counterexample.c: here.
* tests/counterexample.at: Fix expectations.
* src/complain.h, src/complain.c: Add support for -Wcounterexample.
* src/conflicts.c (report_counterexamples): New.
(rule_conflicts_print): Use it when -Wcounterexample is given.
* src/getargs.h, src/getargs.c: Add support for --trace=cex.
* src/main.c (main): Init and deinit counterexample generation.
Vincent ImbimboandAkim Demaille