Use concrete for standard makefile targets
Remove debug branch of process_each_doc

We either will have a deleted doc or not.
Pass revision id to IterFun for open_process_all

This is a non-backwards compatible change since the signature of the
IterFun argument to open_process_all is now:

    `(Key, RevId, Body, Acc)`

Exposing the RevId is important because if you want to later update or
delete the document by talking to couchdb, you need this id to avoid a
round-trip.
Add code comment to open_doc_int
Fix default target of Makefile
Merge branch 'sf/rev_id'