[entropy.client.misc] correct ConfigurationFiles with Python 3

1. Command to execute (diff) was getting arguments like b"path".
2. Crash when priting message.
3. In Python 3, b'x'[0] is int, not str, so a test (if) was (silently)
always true. This way, upon eit commit (at least) and with Python 3,
warning about not merged configuration files was newer printed.

(3) prevented prior discovery of (1) and (2).

Based on my checks, there are no more problems like (3), but I cannot
tell for sure.

lib/entropy/client/misc.py

@@ -184,12 +184,15 @@ class ConfigurationFiles(dict):
         if _vanished():
             return True
 
+        source_unicode = self._unicode_path(source)
+        destination_unicode = self._unicode_path(destination)
+
         # first diff test
         try:
             exit_st = getstatusoutput(
                 'diff -Nua "%s" "%s" | grep '
                 '"^[+-][^+-]" | grep -v \'# .Header:.*\'' % (
-                    source, destination,))[1]
+                    source_unicode, destination_unicode,))[1]
         except (OSError, IOError):
             exit_st = 1
         if exit_st == os.EX_OK:
@@ -204,7 +207,7 @@ class ConfigurationFiles(dict):
                 'egrep \'^[+-]\' | '
                 'egrep -v \'^[+-][\t ]*#|^--- |^\+\+\+ \' | '
                 'egrep -qv \'^[-+][\t ]*$\'' % (
-                    source, destination,), shell = True)
+                    source_unicode, destination_unicode,), shell = True)
         except (IOError, OSError,):
             exit_st = 0
         if exit_st == 1:
@@ -282,8 +285,8 @@ class ConfigurationFiles(dict):
             self._entropy.output(
                 "%s: %s" % (
                     brown(_("Found update")),
-                    self._unicode_path(
-                        darkgreen(filepath)),),
+                    darkgreen(
+                        self._unicode_path(filepath)),),
                 importance = 0,
                 level = "info"
             )
@@ -297,6 +300,7 @@ class ConfigurationFiles(dict):
         # NOTE: with Python 3.x we can remove const_convert...
         # and avoid using _encode_path.
         cfg_pfx = const_convert_to_rawstring("._cfg")
+        underscore = const_convert_to_rawstring("_")
 
         for path in client_conf_protect:
             path = self._encode_path(path)
@@ -323,7 +327,7 @@ class ConfigurationFiles(dict):
                         int(number)
                     except ValueError:
                         continue # not a valid etc-update file
-                    if item[9] != "_": # no valid format provided
+                    if item[9:10] != underscore: # no valid format provided
                         continue
 
                     filepath = os.path.join(currentdir, item)