Fix non-ASCII domain check. (#3727)
Fix non-ASCII domain check. (#3727)

* Fix non-ASCII domain check.

Previously, the code would convert to utf-8, check for non-ASCII, and then try
to use .format() to interpolate the result into an error message. This would
generate a second error that would cause the whole message to get dropped, and
the program to silently exit. The problem can be succinctly observed like so:

$ python
>>> "{0}".format("ウェブ.crud.net")
'\xe3\x82\xa6\xe3\x82\xa7\xe3\x83\x96.crud.net'
>>> "{0}".format(u"ウェブ.crud.net")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-2: ordinal not in range(128)

Note for the curious: This problem only seems to happen with .format():

>>> "%s" % ("ウェブ.crud.net")
'\xe3\x82\xa6\xe3\x82\xa7\xe3\x83\x96.crud.net'
>>> "%s" % (u"ウェブ.crud.net")
u'\u30a6\u30a7\u30d6.crud.net'
stweil/letsencrypt,lmcro/letsencrypt,stweil/letsencrypt,letsencrypt/letsencrypt,letsencrypt/letsencrypt,jsha/letsencrypt,lmcro/letsencrypt,jsha/letsencrypt