Stop using GetHashCode() in PropertyNameMarker

[cdeutsch]

Ran into a weird bug today where I suddenly started getting the error:
"System.ArgumentException: An item with the same key has already been added."

Tracked it back to a GetHashCode() collision in PropertyNameMarker.cs
https://github.com/elasticsearch/elasticsearch-net/blob/develop/src/Nest/Domain/Marker/PropertyNameMarker.cs#L63

...when ElasticTypeConvert.cs is building a Dictionary<PropertyNameMarker, IElasticType> :
https://github.com/elasticsearch/elasticsearch-net/blob/1.2.1/src/Nest/Resolvers/Converters/ElasticTypeConverter.cs#L183

I'm not sure why you need to use GetHashCode() here. Seems like the "Name" property should already be unique.

Here are the two Names that are colliding for me.
-508464000
-509414400

Both strings return: -1595685939

https://www.dropbox.com/s/dx5349ppkimj7ov/Screenshot%202014-10-30%2021.51.46.png?dl=0

[Mpdreamz]

How horribly embarrassing our equals routines ended up doing hashcode != hashcode comparisons on string. I wrote tests for all classes that override Equals() and this should now be fixed.

👍 👍 for reporting.