py3: make sure we open the file in bytes mode

# skip-blame because we are just adding b

Differential Revision: https://phab.mercurial-scm.org/D2077

tests/test-check-help.t

@@ -12,7 +12,7
   > topics = set()
   > topicre = re.compile(br':hg:`help ([a-z0-9\-.]+)`')
   > for fname in sys.argv:
-  >     with open(fname) as f:
+  >     with open(fname, 'rb') as f:
   >         topics.update(m.group(1) for m in topicre.finditer(f.read()))
   > for s in sorted(topics):
   >     print(s)

tests/test-conflict.t

@@ -138,7 +138,7 Verify line trimming of custom conflict
 
   $ hg up -q --clean .
   $ $PYTHON <<EOF
-  > fp = open('logfile', 'w')
+  > fp = open('logfile', 'wb')
   > fp.write(b'12345678901234567890123456789012345678901234567890' +
   >          b'1234567890') # there are 5 more columns for 80 columns
   >