Add missing suspendRelationshipsObservers for belongsTo in DS.RelationshipChangeRemove

[sandstrom]

Fixes a bug where relationship observers aren't suspended for removal of 1-1 relationships, which puts ember into an infinite loop when the removal is synchronised.

This should solve #671.

I think this is just an oversight, since observers are suspended for all other types of relationship changes (see below):

DS.RelationshipChangeRemove.prototype.changeType = "remove";
DS.RelationshipChangeRemove.prototype.sync = function() {
  var secondRecordName = this.getSecondRecordName(),
      firstRecordName = this.getFirstRecordName(),
      firstRecord = this.getFirstRecord(),
      secondRecord = this.getSecondRecord();

  //Ember.assert("You specified a hasMany (" + hasManyName + ") on " + (!belongsToName && (newParent || oldParent || this.lastParent).constructor) + " but did not specify an inverse belongsTo on " + child.constructor, belongsToName);
  //Ember.assert("You specified a belongsTo (" + belongsToName + ") on " + child.constructor + " but did not specify an inverse hasMany on " + (!hasManyName && (newParent || oldParent || this.lastParentRecord).constructor), hasManyName);

  var transaction = this.ensureSameTransaction(firstRecord, secondRecord, secondRecordName, firstRecordName);
  transaction.relationshipBecameDirty(this);

  this.callChangeEvents();

  if (secondRecord && firstRecord) {
    if(this.secondRecordKind === "belongsTo"){
        // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
        set(secondRecord, secondRecordName, null); // <======= OBSERVERS AREN'T SUSPENDED
        // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
     }
     else if(this.secondRecordKind === "hasMany"){
       secondRecord.suspendRelationshipObservers(function(){
        get(secondRecord, secondRecordName).removeObject(firstRecord);
      });
    }
  }

  if (firstRecord && get(firstRecord, firstRecordName)) {
    if(this.firstRecordKind === "belongsTo"){
      firstRecord.suspendRelationshipObservers(function(){
        set(firstRecord, firstRecordName, null);
      });
     }
     else if(this.firstdRecordKind === "hasMany"){
       firstRecord.suspendRelationshipObservers(function(){
        get(firstRecord, firstRecordName).removeObject(secondRecord);
      });
    }
  }

  this.coalesce();
};

[hilem]

this fixed my issue! +1 (beer)