Merge r822458 from trunk:

Work around broken cache management in mod_ldap: If LDAPSharedCacheSize is too
small, try to free some memory by purging the cache and log a warning.

Also increase the default LDAPSharedCacheSize to 500000. This is a more
realistic size suitable for the default values of 1024 for LdapCacheEntries and
LdapOpCacheEntries.

PR: 46749

Submitted by: sf
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@892257 13f79535-47bb-0310-9956-ffa450edef68