After 1a3e8db28d49, Windows XP could not os.stat at all due to raising
immediately when GetFinalPathNameByHandle wasn't available (pre-Vista).
The proper behavior in that situation is to just not attempt a traversal
rather than outright rejecting.
This change additionally handles a failed malloc by setting the error code
and returning false.
Patch by Hirokazu Yamamoto.
Use of DeviceIoControl to obtain the symlink path via the reparse tag was
removed. The code now uses GetFinalPathNameByHandle in the case of a
symbolic link and works properly given the added test which creates a symbolic
link and calls os.stat on it from multiple locations.
Victor Stinner also noticed an issue with os.lstat following the os.stat
code path when being passed bytes. The posix_lstat function was adjusted to
properly hook up win32_lstat instead of the previous STAT macro (win32_stat).
Rather than wrapping the C _isdir function in a Python function,
just import the C _isdir function directly. Additionally, add in the
docstring which was left out.
By changing to the Windows GetFileAttributes API in nt._isdir we can figure
out if the path is a directory without opening the file via os.stat. This has
the minor benefit of speeding up os.path.isdir by at least 2x for regular
files and 10-15x improvements were seen on symbolic links (which opened the
file multiple times during os.stat). Since os.path.isdir is used in
several places on interpreter startup, we get a minor speedup in startup time.
