bpo-34604: Use %R because of invisible characters or trailing whitespaces. (GH-9165)

Misc/NEWS.d/next/Library/2018-09-07-10-16-34.bpo-34604.xL7-kG.rst

 Fix possible mojibake in the error message of `pwd.getpwnam` and
-`grp.getgrnam`. Patch by William Grzybowski.
+`grp.getgrnam` using string representation because of invisible characters
+or trailing whitespaces. Patch by William Grzybowski.

Modules/grpmodule.c

@@ -247,7 +247,7 @@ grp_getgrnam_impl(PyObject *module, PyObject *name)
             PyErr_NoMemory();
         }
         else {
-            PyErr_Format(PyExc_KeyError, "getgrnam(): name not found: %S", name);
+            PyErr_Format(PyExc_KeyError, "getgrnam(): name not found: %R", name);
         }
         goto out;
     }

Modules/pwdmodule.c

@@ -257,7 +257,7 @@ pwd_getpwnam_impl(PyObject *module, PyObject *name)
         }
         else {
             PyErr_Format(PyExc_KeyError,
-                         "getpwnam(): name not found: %S", name);
+                         "getpwnam(): name not found: %R", name);
         }
         goto out;
     }