Reject uploads with Multi-Arch: no

Multi-Arch: no currently breaks wanna-build. We don't want that to happen.

Reference: https://bugs.debian.org/768353

daklib/checks.py

@@ -361,6 +361,11 @@ class BinaryCheck(Check):
                 except:
                     raise Reject('{0}: APT could not parse {1} field'.format(fn, field))
 
+        # "Multi-Arch: no" breaks wanna-build, #768353
+        multi_arch = control.get("Multi-Arch")
+        if multi_arch == 'no':
+            raise Reject('{0}: Multi-Arch: no support in Debian is broken (#768353)'.format(fn))
+
 class BinaryTimestampCheck(Check):
     """check timestamps of files in binary packages