fsmonitor: fix traceback about bytes and str incompatibility

This didn't work anymore in Python 3, switching to a `repr` based reporting does

Differential Revision: https://phab.mercurial-scm.org/D11708

hgext/fsmonitor/__init__.py

@@ -560,8 +560,8 b' def overridestatus('
             for i, (s1, s2) in enumerate(zip(l1, l2)):
                 if set(s1) != set(s2):
                     f.write(b'sets at position %d are unequal\n' % i)
-                    f.write(b'watchman returned: %s\n' % s1)
-                    f.write(b'stat returned: %s\n' % s2)
+                    f.write(b'watchman returned: %r\n' % s1)
+                    f.write(b'stat returned: %r\n' % s2)
         finally:
             f.close()