Support newer leveldb versions (1.18) from google repo

[cupuyc]

I would like to use leveldb 1.18 version from https://github.com/google/leveldb repository.
Current 1.8 leveldb has corruption issue on Mac when process terminated with SIGKILL, which is fixed in 1.18.

When I try to use leveldb from google repo, I get on Mac in mvn clean install -P download -P osx:

[INFO] libtool: compile:  g++ -DHAVE_CONFIG_H -I. -I./src -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk -arch x86_64 -arch i386 -g -O2 -I/Users/stan/work/leveldb/testbuild-1.19/leveldb-1.19/include -I/Library/Java/JavaVirtualMachines/jdk1.8.0_74.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/jdk1.8.0_74.jdk/Contents/Home/include/darwin -c src/leveldbjni.cpp  -fno-common -DPIC -o src/.libs/leveldbjni.o
[INFO] src/leveldbjni.cpp:426:35: error: no member named 'ResumeCompactions' in 'leveldb::DB'
[INFO]         ((leveldb::DB *)(intptr_t)arg0)->ResumeCompactions();
[INFO]         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  ^
[INFO] src/leveldbjni.cpp:435:35: error: no member named 'SuspendCompactions' in 'leveldb::DB'
[INFO]         ((leveldb::DB *)(intptr_t)arg0)->SuspendCompactions();
[INFO]         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  ^
[INFO] 2 errors generated.
[INFO] make: *** [src/leveldbjni.lo] Error 1
[INFO] rc: 2