Use bitset operations when possible, not loops over bits.

Use bitset operations when possible, not loops over bits.
* src/conflicts.c (set_conflicts, count_sr_conflicts): Use
bitset_or.
* src/print.c (print_reductions): Use bitset_and, bitset_andn.
* src/reduce.c (useless_nonterminals): Formatting changes.
* src/warshall.c (TC): Use bitset_or.