First pass clean reading API.

* include/abg-reader.h (read_file): Remove extraneous file parameter.
	* src/abg-reader.cc: Same.
	* tests/test-read-write.cc: Adjust.

include/abg-reader.h

@@ -31,7 +31,7 @@ namespace abigail
 namespace reader
 {
   bool 
-  read_file(const std::string& file_path, translation_unit& tu);
+  read_file(translation_unit& tu);
 }// end namespace reader
 }// end namespace abigail
 

src/abg-reader.cc

@@ -486,10 +486,9 @@ static bool	handle_function_template_decl(read_context&);
 static bool	handle_class_template_decl(read_context&);
 
 bool
-read_file(const string&	file_path,
-	  translation_unit&	tu)
+read_file(translation_unit& tu)
 {
-  read_context read_ctxt(xml::new_reader_from_file(file_path));
+  read_context read_ctxt(xml::new_reader_from_file(tu.get_path()));
 
   return read_input(read_ctxt, tu);
 }

tests/test-read-write.cc

@@ -144,7 +144,7 @@ main()
       string input_suffix(s->in_path);
       in_path = abigail::tests::get_src_dir() + "/tests/" + input_suffix;
       abigail::translation_unit tu(input_suffix);
-      if (!abigail::reader::read_file(in_path, tu))
+      if (!abigail::reader::read_file(tu))
 	{
 	  cerr << "failed to read " << in_path << "\n";
 	  is_ok = false;

tests/test-walker.cc

@@ -50,7 +50,7 @@ main(int argc, char **argv)
   string file_name = argv[1];
 
   abigail::translation_unit tu(file_name);
-  if (!abigail::reader::read_file(file_name, tu))
+  if (!abigail::reader::read_file(tu))
     {
       cerr << "failed to read " << file_name << "\n";
       return 1;