Backport change from trunk:
backends/remote/remote-database.cc: Make the UnimplementedError for a
MatchSpy which doesn't implement name() clearer that it's this
particular subclass which can't be used remotely, not all MatchSpy
objects.

git-svn-id: file:///home/xapian-svn/xapian/branches/1.2@17006 6b2f1b92-a4f3-0310-943f-de3cbe41748b