When a key is mutated change the deleted field to false

We want to do this because we only want to show that a key
is in the deleted state if it doesn't exist in Couchbase.
Lets say a key is being watched for multiple cas values
and then that key gets deleted. We will record deleted
on all of that key's observed cas values. If a user later
sets a key in the database with the same key name then the
deleted state will be cleared and replaced with mutated.

Change-Id: I53337ba355d7196a6f7234b9990125e761af51eb
Reviewed-on: http://review.couchbase.org/10374
Reviewed-by: Steve Yen <steve.yen@gmail.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>

observe_registry.cc

@@ -325,6 +325,7 @@ void VBObserveSet::keyEvent(const std::string &key, const uint64_t cas,
         } else if (itr->key.compare(key) == 0 && itr->cas != cas &&
                    event == OBS_MODIFIED_EVENT) {
             itr->mutated = true;
+            itr->deleted = false;
         } else if (itr->key.compare(key) == 0 && itr->cas == cas) {
             if (event == OBS_PERSISTED_EVENT) {
                 itr->persisted = true;