What steps will reproduce the problem?

1. Write a simple program calling os.Open and exiting. Run it on Windows while
monitoring it with procmon (or alternatively, read the code).

What is the expected output?

A single CreateFile system call.

What do you see instead?

Two CreateFile calls.

Which operating system are you using?

Windows 7

Which version are you using?  (run 'go version' or 'gccgo --version')

changeset:   19292:65546d299e5a
user:        Josh Bleecher Snyder <josharian@gmail.com>
date:        Wed Feb 26 12:25:13 2014 -0800
summary:     cmd/gc: fix bad checknil with ints on 32 bit compilers

Please provide any additional information below.

This is caused by Open() in file_windows.go calling openDir() first then openFile().
There is a brainman comment saying:

  // TODO(brainman): not sure about my logic of assuming it is dir first, then fall back to file

There is no way to avoid 2 system calls in all cases, but I think opening a file should
be tried before opening a directory. I do not recall having used the latter (but maybe
it is used internally). I have no concrete problem or benchmark about this.

Switching the calls, and returning the file error when both openFile and openDir fail
fixes the issue and pass all tests. I do not think openFile might succeed where openDir
did before. Reading:

  http://msdn.microsoft.com/en-us/library/windows/desktop/aa363858(v=vs.85).aspx

The only place mentioning directory handle is the dwFlagsAndAttributes section, about
FILE_FLAG_BACKUP_SEMANTICS, which is never used by syscall.Open().

 I can submit a CL if you want.