Remove quotes from variables names in %define directives and from

Remove quotes from variables names in %define directives and from
qualifiers in %code directives, and restrict the characters that are
allowed in them to M4-friendly ones.  For %define, continue to support
the quoted form as a deprecated feature.  Discussed starting at
<http://lists.gnu.org/archive/html/bison-patches/2007-01/msg00023.html>.
* NEWS (2.3a+): Add entry for the change to %define.  Update entry for
%code.
* doc/bison.texinfo (Prologue Alternatives): Update.
(Bison Declaration Summary): In %defines entry, update mention of
`%code requires' and `%code provides'.
(C++ Location Values): Update %define uses.
(Calc++ Parser Interface): Likewise.
(Calc++ Parser): Likewise, and update `%code requires' uses.
(Bison Symbols): Update %code documentation.
* src/parse-gram.y (prologue_declaration): For %define variables, use
`variable' instead of `STRING'.
(grammar_declaration): For %code qualifiers, use `ID' instead of
`STRING'.
(variable): New nonterminal that takes an `ID' or a `STRING'.
* tests/actions.at (_AT_CHECK_PRINTER_AND_DESTRUCTOR): Update %code
and %define uses.
* tests/calc.at (_AT_DATA_CALC_Y): Update %define use.
* tests/input.at (Reject unused %code qualifiers): Update %code uses.
(%define errors): Update %define uses.