Fix spurious declarations of new merge conflicts

This patch also adds extra tests of the key tree merging logic as well
as edoc-formatted documentation for the module and a few of the merge
functions.  Closes COUCHDB-902.

Thanks Paul Davis, Bob Dionne, Klaus Trainer.

git-svn-id: https://svn.apache.org/repos/asf/couchdb/trunk@1065471 13f79535-47bb-0310-9956-ffa450edef68

apps/couch/src/couch_key_tree.erl

@@ -61,6 +61,7 @@
 
 % partial trees arranged by how much they are cut off.
 
+%% @doc Merge a path with a list of paths and stem to the given length.
 -spec merge([path()], path(), pos_integer()) -> {[path()],
     conflicts | no_conflicts}.
 merge(Paths, Path, Depth) ->