posix: use open() instead of file()

posix: use open() instead of file()

--- a/mercurial/posix.py	Sun Mar 19 01:05:28 2017 -0400
+++ b/mercurial/posix.py	Sun Mar 19 01:05:48 2017 -0400
@@ -181,7 +181,7 @@
                     except OSError as e:
                         if e.errno != errno.ENOENT:
                             raise
-                        file(checknoexec, 'w').close() # might fail
+                        open(checknoexec, 'w').close() # might fail
                         m = os.stat(checknoexec).st_mode
                     if m & EXECFLAGS == 0:
                         # check-exec is exec and check-no-exec is not exec