Don't impose std::string for filenames.

* data/lalr1.cc (b4_filename_type): New.
(position::filename): Use it.
(parser.hh): Move the inclusion of stack.hh and location.hh below
the user code, so that needed headers for the filename type can be
included first.
Forward declare them before the user code.
* tests/Makefile.am (check-local, installcheck-local): Pass
TESTSUITEFLAGS to the TESTSUITE.

data/lalr1.cc

@@ -125,6 +125,12 @@ b4_copyright([C++ Skeleton parser for LALR(1) parsing with Bison],
 /* Using locations.  */
 #define YYLSP_NEEDED ]b4_locations_flag[
 
+namespace yy
+{
+  class position;
+  class location;
+}
+
 ]b4_token_defines(b4_tokens)[
 
 /* Copy the first part of user declarations.  */