Make callback unit test pass for PHP backend.

Deprecated %callback(1) doesn't work with PHP, use "%s" to give the same name
to the callback as to the C function explicitly instead.

Examples/test-suite/callback.i

@@ -1,10 +1,18 @@
 %module callback
 
+// Not specifying the callback name is only possible in Python.
+#ifdef SWIGPYTHON
 %callback(1) foo;
 %callback(1) foof;
 %callback(1) A::bar;
 %callback(1) A::foom;
-%callback("%s_Cb_Ptr") foo_T;  // old style, still works.
+#else
+%callback("%s") foo;
+%callback("%s") foof;
+%callback("%s") A::bar;
+%callback("%s") A::foom;
+#endif
+%callback("%s_Cb_Ptr") foo_T;  // this works in Python too
 
 %inline %{
 

Examples/test-suite/php/Makefile.in

@@ -10,6 +10,7 @@ top_srcdir   = @top_srcdir@
 top_builddir = @top_builddir@
 
 CPP_TEST_CASES += \
+	callback \
 	php_iterator \
 	php_namewarn_rename \