win32: optimize parameters for the CreateFile call in _getfileinfo

Set dwDesiredAccess to 0 instead of GENERIC_READ.
Zero is  enough for querying the file metadata. We don't even need to
access the -contents- of the file.

Set dwShareMode to FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE
instead of the overly restrictive FILE_SHARE_READ.
There is no need to cause write or delete accesses by other processes to
fail while we are querying file metadata.

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

mercurial/win32.py

@@ -31,8 +31,9 b' def os_link(src, dst):'
 def _getfileinfo(pathname):
     """Return number of hardlinks for the given file."""
     try:
-        fh = win32file.CreateFile(pathname,
-            win32file.GENERIC_READ, win32file.FILE_SHARE_READ,
+        fh = win32file.CreateFile(pathname, 0,
+            win32file.FILE_SHARE_READ | win32file.FILE_SHARE_WRITE |
+            win32file.FILE_SHARE_DELETE,
             None, win32file.OPEN_EXISTING, 0, None)
     except pywintypes.error:
         raise OSError(errno.ENOENT, 'The system cannot find the file specified')