Handle FreeDB server errors gracefully (#304)

* handle FreeDB server errors gracefully

In my repeated tests, I ended up upsetting freedb.org, which started
issuing 502 errors. Those errors are not correctly caught by the
program which just crashes with a backtrace. Instead, we handle those
like any other API error, which can already be generated by
perform_lookup (but not handled).

The visible result for the user is that the CD is simply not found on
FreeDB, an acceptable compromise, in my opinion.

Closes: #206

* harmonize an error message with other warnings

... which are all capitalized.

whipper/common/program.py

@@ -251,10 +251,13 @@ class Program:
             logger.debug('CDDB query result: %r', md)
             return [item['DTITLE'] for item in md if 'DTITLE' in item] or None
 
+        except ValueError as e:
+            self._stdout.write("WARNING: CDDB protocol error: %s\n" % e)
+
         except IOError as e:
             # FIXME: for some reason errno is a str ?
             if e.errno == 'socket error':
-                self._stdout.write("Warning: network error: %r\n" % (e, ))
+                self._stdout.write("WARNING: CDDB network error: %r\n" % (e, ))
             else:
                 raise