Replace %push-parser' and %push-pull-parser' with

`%define push_pull "push"' and `%define push_pull "both"'.
`%define push_pull "pull"' is the default.
* doc/bison.texinfo (Push Decl, Push Parser Function,
Pull Parser Function, Parser Create Function, Parser Delete Function):
Update declarations.
(Decl Summary, Table of Symbols): Replace %push-parser and
%push-pull-parser entries with a %define push_pull entry.
* data/bison.m4 (b4_percent_define_check_values): New macro.
(b4_pull_if, b4_push_if, b4_use_push_for_pull_if): Move these
definitions...
* data/c.m4 (b4_identification): ... and the YYPUSH and YYPULL cpp
definitions...
* data/push.c: ... to here and compute them from the value of the
%define variable push_pull.
* data/c-skel.m4: Instead of choosing the push.c skeleton for push
parsing requests here...
* data/yacc.c: ... hack this to switch to push.c any time
b4_use_push_pull_flag or the %define variable push_pull is set.  This
will go away when we mv push.c yacc.c.
* data/c++-skel.m4, data/glr.c, data/java-skel.m4: Don't report that
push parsing is not supported since unused %define variables are
reported anyway.
* src/getargs.c, src/getargs.h (pull_parser, push_parser): Remove.
* src/muscle_tab.h (muscle_percent_define_check_values): Update
comments for consistency with b4_percent_define_check_values.
* src/output.c (prepare): Don't insert b4_pull_flag and b4_push_flag
muscles.
* src/parse-gram.y (PERCENT_PUSH_PARSER, PERCENT_PUSH_PULL_PARSER):
Remove.
(prologue_declaration): Remove %push-parser and %push-pull-parser
rules.
* src/scan-gram.l (%push-parser, %push-pull-parser): Remove rules.
* tests/calc.at: Update declarations.
* tests/input.at (%define enum variables): New test case.
* tests/push.at (Push Parsing: Memory Leak for Early Deletion): Update
declaration.
(Push Parsing: Multiple impure instances): Update declaration.
(Push Parsing: Unsupported Skeletons): New test case.
* tests/torture.at (Exploding the Stack Size with Alloca): Update
declaration.
(Exploding the Stack Size with Malloc): Update declaration.

src/muscle_tab.h

@@ -156,15 +156,17 @@ bool muscle_percent_define_flag_if (char const *variable);
    suspect that the value has yet influenced the output.  */
 void muscle_percent_define_default (char const *variable, char const *value);
 
-/* VALUES points to a sequence of strings that is partitioned into
-   subsequences by NULL's, one terminating each subsequence.  The last
-   subsequence is followed by a second NULL.  For each subsequence, the first
-   string is the name of a %define variable, and all remaining strings in that
-   subsequence are the valid values for that variable.  Complain if such a
-   variable is undefined (a Bison error since the default value should have
-   been set already) or defined to any other value (possibly a user error).
-   Don't record this as a Bison usage of the variable as there's no reason to
-   suspect that the value has yet influenced the output.  */
+/* Mimic b4_percent_define_check_values in ../data/bison.m4 exactly except that
+   the VALUES structure is more appropriate for C.  That is, VALUES points to a
+   list of strings that is partitioned into sublists by NULL's, one terminating
+   each sublist.  The last sublist is followed by a second NULL.  For each
+   sublist, the first string is the name of a %define variable, and all
+   remaining strings in that sublist are the valid values for that variable.
+   Complain if such a variable is undefined (a Bison error since the default
+   value should have been set already) or defined to any other value (possibly
+   a user error).  Don't record this as a Bison usage of the variable as
+   there's no reason to suspect that the value has yet influenced the
+   output.  */
 void muscle_percent_define_check_values (char const * const *values);
 
 /* Grow the muscle for the %code qualifier QUALIFIER appearing at QUALIFIER_LOC