Add chainstate obfuscation to avoid spurious antivirus detection

Adds an `obfuscate` parameter to `CLevelDBWrapper` and makes use of it
for all new chainstate stores built via `CCoinsViewDB`. Also adds an
`Xor` method to `CDataStream`.

Thanks to @sipa @laanwj @pstratem @dexX7 @KyrosKrane @gmaxwell.

src/Makefile.test.include

@@ -53,6 +53,7 @@ BITCOIN_TESTS =\
   test/hash_tests.cpp \
   test/key_tests.cpp \
   test/limitedmap_tests.cpp \
+  test/leveldbwrapper_tests.cpp \
   test/main_tests.cpp \
   test/mempool_tests.cpp \
   test/miner_tests.cpp \
@@ -72,6 +73,7 @@ BITCOIN_TESTS =\
   test/sighash_tests.cpp \
   test/sigopcount_tests.cpp \
   test/skiplist_tests.cpp \
+  test/streams_tests.cpp \
   test/test_bitcoin.cpp \
   test/test_bitcoin.h \
   test/timedata_tests.cpp \