Auto merge of #2598 - str4d:2074-dbwrapper, r=str4d

Bitcoin 0.12+ dbwrapper improvements

Cherry-picked from the following upstream PRs:

- bitcoin/bitcoin#6650
  - Only refactor - excludes obfuscation
- bitcoin/bitcoin#6777
  - Excluding obfuscation-related changes
- bitcoin/bitcoin#6865
- bitcoin/bitcoin#6823
- bitcoin/bitcoin#6873
- bitcoin/bitcoin#7927
  - Excluding first commit (already included) and second commit (obfuscation-related)
- bitcoin/bitcoin#8467

Part of #2074.

src/Makefile.test.include

@@ -60,6 +60,7 @@ BITCOIN_TESTS =\
   test/getarg_tests.cpp \
   test/hash_tests.cpp \
   test/key_tests.cpp \
+  test/dbwrapper_tests.cpp \
   test/main_tests.cpp \
   test/mempool_tests.cpp \
   test/miner_tests.cpp \