Use svntest.main.file_write to avoid end of line conversion.

* subversion/tests/cmdline/blame_tests.py (blame_youngest_to_oldest)

Reported by: jcorvel

Index: subversion/tests/cmdline/blame_tests.py
===================================================================
--- subversion/tests/cmdline/blame_tests.py	(revision 1876706)
+++ subversion/tests/cmdline/blame_tests.py	(working copy)
@@ -958,8 +958,7 @@
   sbox.simple_commit() #r3
 
   # Delete a line.
-  with open(iota_moved, 'w') as f:
-    f.write(line)
+  svntest.main.file_write(iota_moved, line)
   sbox.simple_commit() #r4
 
   expected_output = [