Add Google's LevelDB support

This commit imports LevelDB database sources tree and implements alternative CTxDB storage methods implementation (backported from bitcoin 0.8).

.gitignore

@@ -22,3 +22,5 @@ qrc_*.cpp
 #mac specific
 .DS_Store
 build
+
+!src/leveldb/Makefile

novacoin-qt.pro

@@ -90,6 +90,31 @@ contains(BITCOIN_NEED_QT_PLUGINS, 1) {
     QTPLUGIN += qcncodecs qjpcodecs qtwcodecs qkrcodecs qtaccessiblewidgets
 }
 
+contains(USE_LEVELDB, -) {
+    message(Building without LevelDB)
+    SOURCES += src/txdb-bdb.cpp
+} else {
+    message(Building with LevelDB)
+    DEFINES += USE_LEVELDB
+    INCLUDEPATH += src/leveldb/include src/leveldb/helpers
+    LIBS += $$PWD/src/leveldb/libleveldb.a $$PWD/src/leveldb/libmemenv.a
+    SOURCES += src/txdb-leveldb.cpp
+    !windows {
+        genleveldb.commands = cd $$PWD/src/leveldb ; make libleveldb.a libmemenv.a
+    } else {
+        # make an educated guess about what the ranlib command is called
+        isEmpty(QMAKE_RANLIB) {
+            QMAKE_RANLIB = $$replace(QMAKE_STRIP, strip, ranlib)
+        }
+        genleveldb.commands = cd $$PWD/src/leveldb ; CC=$$QMAKE_CC CXX=$$QMAKE_CXX TARGET_OS=OS_WINDOWS_CROSSCOMPILE CXXFLAGS="-I$$BOOST_INCLUDE_PATH" LDFLAGS="-L$$BOOST_LIB_PATH" make libleveldb.a libmemenv.a ; $$QMAKE_RANLIB $$PWD/src/leveldb/libleveldb.a
+    }
+    genleveldb.target = $$PWD/src/leveldb/libleveldb.a
+    genleveldb.depends = FORCE
+    PRE_TARGETDEPS += $$PWD/src/leveldb/libleveldb.a
+    QMAKE_EXTRA_TARGETS += genleveldb
+    # Gross ugly hack that depends on qmake internals, unfortunately there's no other way to do it.
+    QMAKE_CLEAN += $$PWD/src/leveldb/libleveldb.a; cd $$PWD/src/leveldb ; make clean
+}
 
 # regenerate src/build.h
 !windows|contains(USE_BUILD_INFO, 1) {
@@ -136,6 +161,7 @@ HEADERS += src/qt/bitcoingui.h \
     src/net.h \
     src/key.h \
     src/db.h \
+    src/txdb.h \
     src/walletdb.h \
     src/script.h \
     src/init.h \

src/checkpoints.cpp

@@ -7,7 +7,7 @@
 
 #include "checkpoints.h"
 
-#include "db.h"
+#include "txdb.h"
 #include "main.h"
 #include "uint256.h"