prep for release (2.4.57)

CHANGES

 OpenLDAP 2.4 Change Log
 
-OpenLDAP 2.4.57 Engineering
+OpenLDAP 2.4.57 Release (2021/01/18)
 	Fixed ldapexop to use correct return code (ITS#9417)
 	Fixed slapd to remove asserts in UUIDNormalize (ITS#9391)
 	Fixed slapd to remove assert in csnValidate (ITS#9410)

build/version.var

@@ -18,6 +18,6 @@ ol_minor=4
 ol_patch=X
 ol_api_inc=20456
 ol_api_current=13
-ol_api_revision=4
+ol_api_revision=5
 ol_api_age=11
-ol_release_date="2020/11/10"
+ol_release_date="2021/01/18"