Log Message:
Update to 1.4.18. From the changelog:

indexers:

* omindex:

  + Add default MIME mapping for application/rtf.  IANA have registrations for
    text/rtf and (more recently) application/rtf (it seems because newer
    versions of the RTF format can contain 8-bit data) so we now recognise
    application/rtf by default and handle it the same way as text/rtf.

    Current libmagic seems to always return text/rtf (no matches for
    application/rtf in magic.mgc) and we continue to map extension rtf to
    text/rtf, so this change is mainly future-proofing against libmagic future
    changes.

  + Add support for indexing OpenXPS, which is effectively the same as XPS
    internally in ways we care about, but it uses a different mimetype and a
    different filename extension.

omega:

* Explicitly use OR for MORELIKE queries.

  Since 1.3.0 the default value of DEFAULTOP has been AND, which typically
  makes MORELIKE queries much less useful since they'll only match documents
  containing all the terms from the query expansion.  We now explicitly insert
  " OR " between the terms if DEFAULTOP hasn't been set to OR, which \ 
makes them
  work much more like they did in 1.2.x.

* Make $stoplist and $unstem consider all query strings by always passing the
  new Xapian::QueryParser::FLAG_ACCUMULATE flag.

* Add $foreach command which works like $map, but just concatenates the
  evaluated results rather than adding tabs to turn them into an OmegaScript
  list.

* Extend $include{} to allow handling failure to open the specified file via an
  optional second argument which if specified will be evaluated and returned
  instead.  Patch from Gaurav Arora.

* Support multiple MORELIKE parameters - we now form an RSet from all the
  specified documents and use that to generate the query to run (previously
  only one of multiple MORELIKE parameters was used).