Convert underscores to dashes in some %define variable names.

For now, just api.push-pull and lr.keep-unreachable-states.
Maintain old names for backward compatibility.
* NEWS (2.5): Document.
* data/c.m4 (b4_identification): Update comment.
* data/yacc.c: Update access.
* doc/bison.texinfo: Update.
* etc/bench.pl.in (bench_grammar): Update use.
* src/files.c (tr): Move to...
* src/getargs.c, src/getargs.h (tr): ... here because I can't
think of a better place to expose it.  My logic is that, for all
uses of tr so far, command-line arguments can be involved, and
getargs.h is already included.
* src/main.c (main): Update access.
* src/muscle_tab.c (muscle_percent_define_insert): Convert old
variable names to new variable names before assigning value.
* src/reader.c (reader): Update setting default.
* tests/calc.at: Update uses.
* tests/conflicts.at (Unreachable States After Conflict
Resolution): Update use.
* tests/input.at (%define enum variables): Update use.
(%define backward compatibility): New test group.
* tests/push.at: Update uses.
* tests/reduce.at: Update uses.
* tests/torture.at: Update uses.

src/files.c

@@ -1,7 +1,7 @@
 /* Open and close files for Bison.
 
    Copyright (C) 1984, 1986, 1989, 1992, 2000, 2001, 2002, 2003, 2004,
-   2005, 2006, 2007, 2008 Free Software Foundation, Inc.
+   2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
 
    This file is part of Bison, the GNU Compiler Compiler.
 
@@ -136,15 +136,6 @@ xfclose (FILE *ptr)
 | Compute ALL_BUT_EXT, ALL_BUT_TAB_EXT and output files extensions. |
 `------------------------------------------------------------------*/
 
-/* In the string S, replace all characters FROM by TO.  */
-static void
-tr (char *s, char from, char to)
-{
-  for (; *s; s++)
-    if (*s == from)
-      *s = to;
-}
-
 /* Compute extensions from the grammar file extension.  */
 static void
 compute_exts_from_gf (const char *ext)