ns_server does not issue drop_deletes flag for metadata purge of deleted item.

Steps to reproduce:
0)create default bucket and set the Metadata Purge Interval from UI to 0.04==1hour. No views are created.
1)Insert a document with key "fooaaa". this is inserted in vbucket 14.
2)delete the document.
3) using ./couch_dbdump tool get the document metadata.
./couch_dbdump /opt/couchbase/var/lib/couchbase/data/default/14.couch.1
cas: 18425762490303526, expiry: 1404756141, flags: 0
doc deleted
4)wait for 1 hour and generated workload (with different keys) such that auto compaction is triggered.
5) using ./couch_dbdump tool it is seen that metadata is still present in newly compacted file i.e tombstone was not dropped.
./couch_dbdump /opt/couchbase/var/lib/couchbase/data/default/14.couch.2
cas: 18425762490303526, expiry: 1404756141, flags: 0
doc deleted