AddToWallet implies BindWallet

Now that AddToWallet is called when loading transactions from the
wallet database, BindWallet can be integrated into that and does not
need to be an extra step.

Leaves behaviour unchanged, but makes the
fFromLoadWallet/!fFromLoadWallet paths in AddToWallet a bit more
symmetric.
Also switch the (unused) verification code to low-s instead of even-s.

a81cd968 introduced a malleability breaker for signatures
(using an even value for S). In e0e14e43 this was changed to
the lower of two potential values, rather than the even one.
Only the signing code was changed though, the (for now unused)
verification code wasn't adapted.
Fix script test handling of empty scripts

Previously an empty script would evaluate to OP_0
Test CHECKMULTISIG with m == 0 and n == 0
Fix bloom filter not to use bit_mask
Fix importwallet nTimeFirstKey
gitian: add statically built variant of bitcoind/bitcoin-cli
remove an assignment which is never used.
unified and better log/error messages for CDBEnv/CDB
added many rpc wallet tests

deleted the empty no throw test in rpc_wallet_tests line 65

fixed some comments

starting verify tests

finished verify message tests

changed some comments
[Qt] rescan progress
Add gitian build guide

Work in progress...
Have pull-tester run the listtransactions.py regression test

This should show how to run a python-based regression test
successfully in the pull-tester environment.
Merge pull request #3928

3927836 [Qt] rescan progress (Cozz Lovan)
Merge pull request #3998

cb4bdd1 Have pull-tester run the listtransactions.py regression test (Gavin Andresen)
Merge pull request #3929

4c35366 Fix importwallet nTimeFirstKey (Cozz Lovan)
Merge pull request #3994

2c47a00 Add gitian build guide (Wladimir J. van der Laan)
Merge pull request #3572

f7257cf unified and better log/error messages for CDBEnv/CDB (Philip Kaufmann)
Update README.md
Merge pull request #4005 from Telepatheic/patch-1

Update README.md