tests: force \n newlines when writing to sys.stdout

Without this, Python 3 on Windows inserts some \r that aren't
present in the input, causing test-http-bad-server.t to fail.
After this change, the test passes on Python 3 on Windows!

Differential Revision: https://phab.mercurial-scm.org/D8341

tests/filtertraceback.py

@@ -1,29 +1,40
 #!/usr/bin/env python
 
 # Filters traceback lines from stdin.
 
 from __future__ import absolute_import, print_function
 
+import io
 import sys
 
+if sys.version_info[0] >= 3:
+    # Prevent \r from being inserted on Windows.
+    sys.stdout = io.TextIOWrapper(
+        sys.stdout.buffer,
+        sys.stdout.encoding,
+        sys.stdout.errors,
+        newline="\n",
+        line_buffering=sys.stdout.line_buffering,
+    )
+
 state = 'none'
 
 for line in sys.stdin:
     if state == 'none':
         if line.startswith('Traceback '):
             state = 'tb'
 
     elif state == 'tb':
         if line.startswith('  File '):
             state = 'file'
             continue
 
         elif not line.startswith(' '):
             state = 'none'
 
     elif state == 'file':
         # Ignore lines after "  File "
         state = 'tb'
         continue
 
     print(line, end='')