MODE-2061 Changed UrlBinaryKey to be return hashes that are more consistent with JavaDoc contract.

The `UrlBinaryKey`'s `getHash()` and `getHexHash()` methods were returning values that were the not same size and non characteristic of SHA-1 values. This modification changes these methods to return the SHA-1 of the string form of the URL. This is consistent with the requirements of the methods signatures, and with the equals/compare behavior of how these methods are used within ModeShape: if the hash is the same then it is expected that the binary value is the same.