Speed up most calls to 'stat' and 'lstat' on MS-Windows.
src/w32.c (stat_worker): If w32_stat_get_owner_group is zero, do not
try to get accurate owner and group information from NT file
security APIs. This is to make most callers of 'stat' and
'lstat', which don't need that information, much faster.
src/dired.c (Ffile_attributes) [WINDOWSNT]: Set
w32_stat_get_owner_group to a non-zero value, to request accurate
owner and group information from 'lstat'.