Remove automatic update of default key #3074

This equalizes the behavior between the GUI and bitcoind and removes the last usage of fHaveGui (the other is removed in #3072).

The commit doesn't completely remove default key functionality but removes the code that sets a new default key after a transaction when it received coins. Completely removing default key functionality is not that easy because it is used as stopgap in a few places

• https://github.com/bitcoin/bitcoin/blob/master/src/wallet.cpp#L1453 (in CWallet::LoadWallet) to determine whether this is the first run with this wallet.
• https://github.com/bitcoin/bitcoin/blob/master/src/wallet.cpp#L1837 (in CReserveKey::GetReservedKey) to return something when the keys are exhausted and keypool should be topped up

However these stopgaps are not affected by this change. There will still be an initial default key, it will just never change.

Automatic sanity-testing: PASSED, see http://jenkins.bluematt.me/pull-tester/b0091bb8961eb9c6eda1aabba7182794b3d0d477 for binaries and test log. This test script verifies pulls every time they are updated. It, however, dies sometimes and fails to test properly. If you are waiting on a test, please check timestamps to verify that the test.log is moving at http://jenkins.bluematt.me/pull-tester/current/ Contact BlueMatt on freenode if something looks broken.

ACK unless there is someone depending on this. Perhaps some people are - I don't know.

As this is one way through which "no key reuse" was encouraged, I'm sort-of sad to see this go, though it's unlikely to be a big deal, as the default key isn't shown anywhere.

It wasn't a good feature against key reuse.

• There are concurrency problems waiting for anyone relying on this in larger sites (that means -- anyone waiting for more than one transaction at a time)
• As this is only active in bitcoind and there is no way to interact with the default key at all

I doubt anyone is depending on this.

ACK