(ITS#7361) alock is broken on Windows

[hyc@OpenLDAP.org]

Full_Name: Howard Chu
Version: 2.4.32
OS: 
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (76.94.188.8)
Submitted by: hyc


alock assumes (wrongly) that it can always read from a locked region. That's
true for POSIX advisory locks, but Windows locks are mandatory. I.e., attempting
to read from a region with a write lock returns EACCES.

Because alock doesn't detect this situation correctly, it will end up waiting
forever to acquire a lock on a region that's already locked. (E.g., if slapd is
already running and slapcat is started, slapcat will hang trying to get the
region lock.)

A fix is coming shortly.