* examples/bddcalc/parser.yxx: Rename as ...
* examples/bddcalc/parser.y: ... this.
* examples/bddcalc/parser_.cxx: New file that includes parser.c.
* examples/bddcalc/Makefile.am: Adjust.
* examples/bddcalc/parser.hxx: Delete this unused file.
Get rid of some "deprecated conversion from string constant to
`char*'" warnings.
* examples/bddcalc/parser_.h (yyerror): Declare the format
as a "const char*".
* examples/bddcalc/parser.yxx (yyerror): Likewise.