Python 3 support for certonly

setup.py

@@ -43,7 +43,6 @@ install_requires = [
     'psutil>=2.2.1',  # 2.1.0 for net_connections and 2.2.1 resolves #1080
     'PyOpenSSL',
     'pyrfc3339',
-    'python2-pythondialog>=3.2.2rc1',  # Debian squeeze support, cf. #280
     'pytz',
     # For pkg_resources. >=1.0 so pip resolves it to a version cryptography
     # will tolerate; see #2599:
@@ -53,6 +52,12 @@ install_requires = [
     'zope.interface',
 ]
 
+# Debian squeeze support, cf. #280
+if sys.version_info[0] == 2:
+    install_requires.append('python2-pythondialog>=3.2.2rc1')
+else:
+    install_requires.append('pythondialog>=3.2.2rc1')
+
 # env markers in extras_require cause problems with older pip: #517
 # Keep in sync with conditional_requirements.py.
 if sys.version_info < (2, 7):