Test if getHash is static

[thiemowmde]

This should fix #130.

It turns out PHP's serialize() function just calls the ...->serialize() methods provided by the Serializable interface in Snak. See the implementations in SnakObject::serialize and PropertyValueSnak::serialize. Only properties that are used in these methods become part of the serialization.

This patch:

• Adds tests to make sure the getHash implementation is static and doesn't change, e.g. when new fields are introduced.
• Adds basic tests for No- and SomeValueSnak.
• Removes strange self-comparisons from tests.
• Simplifies some loops.
• Renames some strange variables.

[JeroenDeDauw]

NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!

[JeroenDeDauw]

@thiemowmde sad kittens are sad

[thiemowmde]

Never got an answer to my last question. Seems it's fine to break all our hashing from time to time.

If you ask me it's not better if all hashes break because we reimplement the hash function or if they break because of a namespace change. The later is much more unlikely at this point in time. Coming up with a new hash function will break everything for sure. Just keeping the hash functions as they are will not break anything. Therefor I'm closing this now.