Fix IsInitialBlockDownload which was broken by headers first.
MOVEONLY: Move void UpdateTime() from pow.o to miner.o (plus fix include main.h -> chain.h)
CBlockIndex::GetBlockWork() + GetProofIncrement(nBits) -> GetBlockProof(CBlockIndex)
Update serialize comments to be doxygen compatible
The first thing that SelectParams does is call SelectBaseParams. Therefore, we do not need to call SelectBaseParams immediately prior to calling SelectParams.
[Wallet] Reduce minTxFee for transaction creation to 1000 satoshis
Fix node ranges in the test framework.
Add a locking mechanism to IsInitialBlockDownload to ensure it never goes from false to true.
gather_inputs: use correct variable in error message

"amount" and "fee" do not exist (anymore?).
Do not use third party services for IP detection.

This is a simplified re-do of closed pull #3088.

This patch eliminates the privacy and reliability problematic use
of centralized web services for discovering the node's addresses
for advertisement.

The Bitcoin protocol already allows your peers to tell you what
IP they think you have, but this data isn't trustworthy since
they could lie. So the challenge is using it without creating a
DOS vector.

To accomplish this we adopt an approach similar to the one used
by P2Pool: If we're announcing and don't have a better address
discovered (e.g. via UPNP) or configured we just announce to
each peer the address that peer told us. Since peers could
already replace, forge, or drop our address messages this cannot
create a new vulnerability... but if even one of our peers is
giving us a good address we'll eventually make a useful
advertisement.

We also may randomly use the peer-provided address for the
daily rebroadcast even if we otherwise have a seemingly routable
address, just in case we've been misconfigured (e.g. by UPNP).

To avoid privacy problems, we only do these things if discovery
is enabled.
Make comments in /src/script doxygen compatible
Do signature-s negation inside the tests

To avoid the need for libsecp256k1 to expose such functionality.
Add unauthenticated HTTP REST interface to public blockchain data.
Reset setBlockIndexCandidates once block index db loaded
Merge pull request #5240

5e2dcae gather_inputs: use correct variable in error message (dexX7)
Merge pull request #5161

845c86d Do not use third party services for IP detection. (Gregory Maxwell)
Merge pull request #5256

f4e0aef Do signature-s negation inside the tests (Pieter Wuille)
travis: install less packages from apt-get
travis: attempt to fix unlikely build issue

This is a long chain of errors, and there are likely other changes that could
be made to cope in other places along that chain.

If depends don't build successfully, don't bother trying again for the sake of
better logging. That's likely to hurt more than help. In this case, qt build
failed, and on the second attempt, it appeared to be successful. However, due
to a bad object from an internal gcc error on the first build, the resulting
lib was unusable. This caused bitcoin-qt to not be built, and tests and
packaging which expected bitcoin-qt to be there failed.

The root cause:
Mingw is especially crashy when using -jX, likely compounded by low-memory
environments. I've seen multiple problems with this combo in Gitian as well.

In this case:
i686-w64-mingw32-g++: internal compiler error: Killed (program cc1plus)
...
make[3]: *** [.obj/release/qdrawhelper.o] Error 4

The workaround:
Bump Travis down to using -j2 by default. Additionaly, enable --with-gui for
the windows builds. This will cause configure to fail if qt is not working
while also testing the config flag.

Other failures which may be worth revisiting separately:
- If a depends package fails, maybe remove the workdir so that it doesn't taint
  subsequent runs
- See if there's anything repeatable about the ICE when building qt
depends: cleanup better after qt and force a bump

qt needs to be rebuilt for travis. The previous commit should help ensure that
this won't need to be done again.