Fixes ignored qt 4.8 codecs path on windows when configuring with --with-qt-libdir
[Qt] ensure all class attributes are init to 0

- in BitcoinGUI and UnitDisplayStatusBarControl
[Qt] use BitcoinGUI::DEFAULT_WALLET constant in bitcoin.cpp
[Qt] disable tray interactions when client model set to 0

- this prevents the ability to fiddle around with the system tray when
  already shutting down (e.g. on slow shutdowns because of a proxy delay)
- extends solution for #4360
Add a getutxos command to the p2p protocol. It allows querying of the UTXO set
given a set of outpoints.
Add boolean HaveWatchonly and signal NotifyWatchonlyChanged
[Qt] Add column Watch-only to transactions list
Clean-up SyncWithWallets/SyncTransaction
build: work around ccache/autotools warning-spamming bug

When using clang and ccache, builds spew lots of:
Clang: warning: argument unused during compilation

Upstream bug: https://bugzilla.samba.org/show_bug.cgi?id=8118

This is harmless, bug annoying. If ccache is being used and the
-Qunused-arguments flag is supported (clang), use it.
depends: add a fallback path in case package sources go missing

If a source url fails to download, try again at
$FALLBACK_DOWNLOAD_PATH/file.name, where FALLBACK_DOWNLOAD_PATH can be
overridden by the user.
Move UpdateTime to pow
Move CBlockIndex::GetBlockWork() to pow::GetProofIncrement(nBits)
replace ComputeMinWork with CheckMinWork
Allow BatchWrite to destroy its input, reducing copying
Make CScript::clear() release its memory
Merge pull request #4683

fff7455 Make CScript::clear() release its memory (Pieter Wuille)
b0875eb Allow BatchWrite to destroy its input, reducing copying (Pieter Wuille)
Test IsPushOnly() with invalid push
Merge pull request #4351

da2ec10 Add a getutxos command to the p2p protocol. It allows querying of the UTXO set given a set of outpoints. (Mike Hearn)
Merge pull request #4654

c4a7709 Fixes ignored qt 4.8 codecs path on windows when configuring with --with-qt-libdir (ntrgn)
Merge pull request #4716

0d27dad Clean-up SyncWithWallets/SyncTransaction (Cozz Lovan)