Replace UnicodeDecodeErrors caused by Python2 readline() method.

* CHANGE gnupg._meta.GPGBase.__init__() to register the builtin
   `codecs.replace_errors` handler and a global codecs "strict" error
   handler.
 * FIXES Issue #49:
   https://github.com/isislovecruft/python-gnupg/issues/49

gnupg/_meta.py

@@ -159,6 +159,14 @@ class GPGBase(object):
         self._filesystemencoding = encodings.normalize_encoding(
             sys.getfilesystemencoding().lower())
 
+        # Issue #49: https://github.com/isislovecruft/python-gnupg/issues/49
+        #
+        # During `line = stream.readline()` in `_read_response()`, the Python
+        # codecs module will choke on Unicode data, so we globally monkeypatch
+        # the "strict" error handler to use the builtin `replace_errors`
+        # handler:
+        codecs.register_error('strict', codecs.replace_errors)
+
         self._keyserver = 'hkp://wwwkeys.pgp.net'
         self.__generated_keys = os.path.join(self.homedir, 'generated-keys')