[PATCH] tests: fix import order in test-bdiff

[Martin von Zweigbergk]

# HG changeset patch
# User Martin von Zweigbergk <martinvonz at google.com>
# Date 1484168228 28800
#      Wed Jan 11 12:57:08 2017 -0800
# Node ID 193e2d6cba6f294dca88b939a2a1afa5874a9794
# Parent  9823e2f50a935f6170e01235b65b5282680ebdab
tests: fix import order in test-bdiff

Without this, I see the following failure in
test-check-module-imports.t.

@@ -180,3 +180,5 @@
   > -X tests/test-hgweb-no-request-uri.t \
   > -X tests/test-hgweb-non-interactive.t \
   > | sed 's-\\-/-g' | python "$import_checker" -
+  tests/test-bdiff.py:6: imports not lexically sorted: silenttestrunner < unittest
+  [1]

diff -r 9823e2f50a93 -r 193e2d6cba6f tests/test-bdiff.py
--- a/tests/test-bdiff.py	Sun Jan 08 00:52:54 2017 +0800
+++ b/tests/test-bdiff.py	Wed Jan 11 12:57:08 2017 -0800
@@ -1,10 +1,9 @@
 from __future__ import absolute_import, print_function
 import collections
+import silenttestrunner
 import struct
 import unittest
 
-import silenttestrunner
-
 from mercurial import (
     bdiff,
     mpatch,