api.tokens.prefix -> api.token.prefix

See
http://lists.gnu.org/archive/html/bison-patches/2012-02/msg00045.html
Note that api.tokens.prefix has not been released, yet.

* NEWS, data/bison.m4, doc/bison.texi, tests/c++.at,
* tests/calc.at, tests/java.at, tests/local.at: Do it.
* src/muscle-tab.c (muscle_percent_variable_update): Ensure
backward compatibility.

src/muscle-tab.c

@@ -398,6 +398,7 @@ muscle_percent_variable_update (char const *variable, location variable_loc)
   const conversion_type conversion[] =
     {
       { "api.push_pull", "api.push-pull", },
+      { "api.tokens.prefix", "api.token.prefix", },
       { "location_type", "api.location.type", },
       { "lr.keep_unreachable_states", "lr.keep-unreachable-states", },
       { "namespace", "api.namespace", },