(ITS#4328) improve retry capabilities of back-meta

[ando@sys-net.it]

Full_Name: Pierangelo Masarati
Version: HEAD/re23
OS: irrelevant
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (131.175.154.56)
Submitted by: ando


There appear to be cases where back-meta cannot recover from a remote server
failure even if when it comes back.  This may be related to ITS#4234 and
ITS#4240, but I cannot confirm it, so I'm opening a new ITS.

The fix is about to come. p.