MB-17174 Don't iterate through all headers in db files.
MB-17174 Don't iterate through all headers in db files.

This can get extremely expensive if databases are not regularly
compacted.

Change-Id: I9d6c0810a6e9031832305117f89b40df24085fe9
Reviewed-on: http://review.couchbase.org/58222
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>

membase/ns_server,membase/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,ceejatec/ns_server,ceejatec/ns_server