better error reporting on failed open/fopen

plugins/python/python_plugin.c

@@ -196,7 +196,7 @@ PyObject *uwsgi_pyimport_by_filename(char *name, char *filename) {
 		real_filename = uwsgi_concat2(filename, "/__init__.py");
 		pyfile = fopen(real_filename, "r");
 		if (!pyfile) {
-			uwsgi_error("fopen()");
+			uwsgi_error_open(real_filename);
 			exit(1);
 		}
 	}

plugins/python/uwsgi_pymodule.c

@@ -2087,7 +2087,7 @@ PyObject *py_uwsgi_parse_file(PyObject * self, PyObject * args) {
 
 	fd = open(filename, O_RDONLY);
 	if (fd < 0) {
-		uwsgi_error("open()");
+		uwsgi_error_open(filename);
 		goto clear;
 	}