api/registry.cc,include/xapian/weight.h,tests/api_backend.cc,
tests/api_nodb.cc,tests/api_weight.cc,weight/Makefile.mk,
weight/lmweight.cc: Add Unigram LMWeight class.

git-svn-id: file:///home/xapian-svn/xapian/trunk@18308 6b2f1b92-a4f3-0310-943f-de3cbe41748b
csharp/Makefile.am,java/Makefile.am: Update for addition of LMWeight
class.

git-svn-id: file:///home/xapian-svn/xapian/trunk@18309 6b2f1b92-a4f3-0310-943f-de3cbe41748b
docs/omegascript.rst,weight.cc: Add support for $set{weighting,lm}.

git-svn-id: file:///home/xapian-svn/xapian/trunk@18310 6b2f1b92-a4f3-0310-943f-de3cbe41748b