Fix python2 client compatibility

Python2 ignores the byte string qualification (b’foo’)  but falls over for the combination rb for this regexp. Switching the qualification to br appears to fix this and works in both python2 and python3.

sshuttle/client.py

@@ -299,8 +299,8 @@ class FirewallClient:
             raise Fatal('%r expected STARTED, got %r' % (self.argv, line))
 
     def sethostip(self, hostname, ip):
-        assert(not re.search(rb'[^-\w\.]', hostname))
-        assert(not re.search(rb'[^0-9.]', ip))
+        assert(not re.search(br'[^-\w\.]', hostname))
+        assert(not re.search(br'[^0-9.]', ip))
         self.pfile.write(b'HOST %s,%s\n' % (hostname, ip))
         self.pfile.flush()