omindex.cc,tmpdir.h: Add get_tmpfile() helper function.

git-svn-id: file:///home/xapian-svn/xapian/trunk@17858 6b2f1b92-a4f3-0310-943f-de3cbe41748b
api/replication.cc: Fix conditional for enabling replication code
- if chert is disabled but brass isn't, we should still enable it.

git-svn-id: file:///home/xapian-svn/xapian/trunk@17859 6b2f1b92-a4f3-0310-943f-de3cbe41748b