(ITS#7035) libldap wait4msg loops forever

[hyc@OpenLDAP.org]

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


In test060 slapd-mtread will frequently get into an endless loop if slapd dies
during the multi-threaded reader+writer test. poll() returns a POLL_HANGUP event
but libldap only handles POLL_WRITE and POLL_READ; since nothing handles the
hangup event poll keeps returning the event.

Patch coming shortly.