BIP 32 derivation + test vectors

[sipa]

This does not add actual deterministic wallet functionality yet, only an implementation of BIP32 derivation and its test vectors.

I'm usually not in favor of adding code that isn't used yet, but in this case it may be useful to give a "reference implementation" exposure.

[BitcoinPullTester]

Automatic sanity-testing: PASSED, see http://jenkins.bluematt.me/pull-tester/a59db19ee3b454680b3bb0aa881e601b9311a9ae for binaries and test log.
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[simondlr]

Do you plan on eventually implementing full BIP 32 support into Bitcoin-QT?

[sipa]

@simondlr Of course.

[simondlr]

@sipa Awesome! Looking forward to it.

[sipa]

@gavinandresen @jgarzik @gmaxwell Opinions?

[gmaxwell]

ACK. On the basis that this has already been used to validate other implementations and has even turned up some bugs, I think it would be good to include this.

[jgarzik]

ACK