Fix for GetBlockValue() after block 13,440,000

Forces the block reward to zero when right shift in GetBlockValue() is
undefined, after 64 reward halvings (block height 13,440,000).
Fix importwallet nTimeFirstKey
remove an assignment which is never used.
unified and better log/error messages for CDBEnv/CDB
[Qt] rescan progress
Add gitian build guide

Work in progress...
Edit subsidy_limit_test to account for BIP42

Because no one wants 4 gold mines being discovered every mibillenium.
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 #3842 from ditto-b/master

Fix for GetBlockValue() after block 13,440,000
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
Move assert(pindexNew); to above where we dereference pindexNew.
Merge pull request #4010

94c8bfb Move assert(pindexNew); to above where we dereference pindexNew. (Gregory Maxwell)
Merge pull request #3972

fbf617a remove an assignment which is never used. (Yoichi Hirai)