Test annotation parsing: strip line endings

Since annotation parsing opens the file in byte mode, carriage returns are not
stripped away, and can ultimately be included as part of an annotation's data.

A consequence of this is that `DMLC-FLAG` will pass stray carriage returns to
DMLC on Windows. mini-python will apparently discard these, but Pypy *doesn't*,
and that can cause parsing of the flag to fail.

The fix to this is to strip away any line endings explicitly.

test/tests.py

@@ -526,7 +526,7 @@ def test_flags(self, filename=None, append_to=None):
         else:
             flags = append_to
         for (linenum, line) in enumerate(open(filename, "rb"), 2):
-            m = annotation_re.match(line)
+            m = annotation_re.match(line.rstrip(b'\r\n'))
             if not m:
                 continue
             (key, data) = m.groups()