List accepted values for a %define enum variable with an invalid value.

List accepted values for a %define enum variable with an invalid value.

Suggested by Akim Demaille at
<http://lists.gnu.org/archive/html/bison-patches/2009-04/msg00082.html>.
* data/bison.m4 (_b4_percent_define_check_values): Implement.
* src/muscle_tab.c (muscle_percent_define_check_values): Implement.
* tests/input.at (%define lr.default_reductions invalid values): Merge
into...
(%define enum variables): ... here, and update output.