fix libleveldb error when compiling on linux

When compiling on Linux, I was getting this error:

    g++: error: /home/arthur/tmp/frozencoin/src/leveldb/libleveldb.a: No such file or directory
    g++: error: /home/arthur/tmp/frozencoin/src/leveldb/libmemenv.a: No such file or directory
    make: *** [frozen-qt] Error 1

so I looked at how other coins source and grabbed what was missing. :)