Merge branch 'match_newlines_py3' into 'master'

Fix inconsistent newlines read from a file in python3

Closes #457

See merge request pycqa/flake8!253

src/flake8/processor.py

@@ -1,6 +1,5 @@
 """Module containing our file processor that tokenizes a file for checks."""
 import contextlib
-import io
 import logging
 import sys
 import tokenize
@@ -308,11 +307,9 @@ class FileProcessor(object):
     def _readlines_py3(self):
         # type: () -> List[str]
         try:
-            with open(self.filename, "rb") as fd:
-                (coding, lines) = tokenize.detect_encoding(fd.readline)
-                textfd = io.TextIOWrapper(fd, coding, line_buffering=True)
-                return [l.decode(coding) for l in lines] + textfd.readlines()
-        except (LookupError, SyntaxError, UnicodeError):
+            with tokenize.open(self.filename) as fd:
+                return fd.readlines()
+        except (SyntaxError, UnicodeError):
             # If we can't detect the codec with tokenize.detect_encoding, or
             # the detected encoding is incorrect, just fallback to latin-1.
             with open(self.filename, encoding="latin-1") as fd: