There's a tab, rather than a space, in the second-last line of schema.OpenLDAP.  It turns out that the RFC syntax for the corresponding .ldif files <https://tools.ietf.org/html/rfc2849> (or at least the OpenLDAP interpretation of it) is rather... unimaginative about what counts as 'whitespace'.

(Sorry for reporting this as two separate bugs -- this and #839: I thought the fix in #839 had resulted in a working .ldif file, but this turned out to be an artefact of the preprocessing I was doing to turn schema.OpenLDAP into the appropriate .ldif for upload, and when I tweaked that this problem emerged.  This problem is of course trivial to fix in practice, but it seems worthwhile reporting and fixing, since the error OpenLDAP reports bears absolutely _no_ resemblance to the actual problem, which results in a certain amount of hair torn out.)