* src/gram.h, src/gram.c (error_token_number): Remove, use

errtoken->number.
* src/reader.c (reader): Don't specify the user token number (2)
for $undefined, as it uselessly prevents using it.
* src/gram.h (token_number_t): Move to...
* src/symtab.h: here.
(state_t.number): Is a token_number_t.
* src/print.c, src/reader.c: Use undeftoken->number instead of
hard coded 2.
(Even though this 2 is not the same as above: the number of the
undeftoken remains being 2, it is its user token number which
might not be 2).
* src/output.c (prepare_tokens): Rename the `maxtok' muscle with
`user_token_number_max'.
Output `undef_token_number'.
* data/bison.simple, data/bison.c++: Use them.
Be sure to map invalid yylex return values to
`undef_token_number'.  This saves us from gratuitous SEGV.
* tests/conflicts.at (Solved SR Conflicts)
(Unresolved SR Conflicts): Adjust.
* tests/regression.at (Web2c Actions): Adjust.

tests/regression.at

@@ -336,8 +336,8 @@ $ (0) 0
 ';' (59) 5
 '=' (61) 5
 error (256)
-undef_id_tok (257) 5
-const_id_tok (258) 5
+undef_id_tok (258) 5
+const_id_tok (259) 5
 Nonterminals, with rules where they appear
 $axiom (7)
     on left: 0
@@ -460,8 +460,8 @@ AT_CHECK([[sed -n 's/  *$//;/^static const.*\[\] =/,/^}/p' input.c]], 0,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
        2,     2,     2,     2,     2,     2,     2,     2,     2,     2,
-       2,     2,     2,     2,     2,     2,     1,     3,     4,     5,
-       6
+       2,     2,     2,     2,     2,     2,     1,     2,     3,     4,
+       5,     6
 };
 static const short yyprhs[] =
 {
@@ -483,7 +483,7 @@ static const char *const yytname[] =
 };
 static const short yytoknum[] =
 {
-       0,   256,     2,   257,   258,   259,   260,    -1
+       0,   256,   257,   258,   259,   260,   261,    -1
 };
 static const short yyr1[] =
 {