Fix IsInitialBlockDownload which was broken by headers first.
[Wallet] Reduce minTxFee for transaction creation to 1000 satoshis
Add a locking mechanism to IsInitialBlockDownload to ensure it never goes from false to true.
Reset setBlockIndexCandidates once block index db loaded
Win32: log addresses found in Discover() calls
Win32: change buffer size for gethotsname in Discover()

- 256 byte is the maximum, as per
  http://msdn.microsoft.com/en-us/library/windows/desktop/ms738527%28v=vs.85%29.aspx
Abstract context-dependent block checking from acceptance
CreateNewBlock and miner_tests: Also check generated template is valid by CheckBlockHeader, ContextualCheckBlockHeader, CheckBlock, and ContextualCheckBlock
TestBlockValidity function for CBlock proposals (used by CreateNewBlock)
miner_tests: Disable checkpoints so they don't fail the subsidy-change test
Abstract DecodeHexBlk and BIP22ValidationResult functions out of submitblock
Implement BIP 23 Block Proposal
QA RPC tests: Add tests block block proposals
submitblock: Check for duplicate submissions explicitly
depends: Use pic for all linux dependencies

This avoids textrels, and matches previous gitian behavior.
depends: Add a package for qt4.6. Linux uses it by default.

We're not ready to switch to a static qt5 for Linux yet due to missing plugin
support. This adds a recipe for building a shared qt4 that we build and link
against, but don't distribute.

make USE_LINUX_STATIC_QT5=1 can be used to build static qt5 as before.
gitian: descriptors overhaul

Descriptors now make use of the dependencies builder, so results are cached.
A very new version (>= e9741525c) of Gitian should be used in order to take
advantage of caching.
gitian: quick docs update
travis: let travis use shared libs for tests
gitian: make tarballs deterministic and nuke .la files from build output