Fixed compile warning on Mac caused by unused variables.

Summary:
Fixed compile warning caused by unused variables.

./db/compaction_picker.h:118:7: error: private field 'max_grandparent_overlap_factor_' is not used [-Werror,-Wunused-private-field]
  int max_grandparent_overlap_factor_;
      ^
./db/compaction_picker.h:119:7: error: private field 'expanded_compaction_factor_' is not used [-Werror,-Wunused-private-field]
  int expanded_compaction_factor_;
      ^
2 errors generated.

Test Plan:
make db_test
Fixed signed-unsigned comparison warning in db_test.cc

Summary:
Fixed signed-unsigned comparison warning in db_test.cc

db/db_test.cc:8606:3: note: in instantiation of function template specialization 'rocksdb::test::Tester::IsEq<int, unsigned long>' requested here
  ASSERT_EQ(2, metadata.size());
    ^

Test Plan:
make db_test
Merge pull request #329 from fyrz/master

resolution for java build problem introduced by 5ec53f3edf62bec1b690ce12...
Column family support in RocksJava

This commit includes the support for the following functionalities:
  - Single Get/Put operations
  - WriteBatch operations
  - Single iterator functionality
  - Open database with column families
  - Create column family
  - Drop column family
  - Properties of column families
  - Listing of column families

In addition there is an additional Java sample which can be build
using "make cfsample".

What is not supported currently using RocksJava:
  - Multi Iterator support
  - MultiGet

I decided to file a pull request w/o the missing two features to omit
some merging trouble. I would propose to hand them over to a later point
of time.
Quality improvements
- Replaced all NULL occurences in code with nullptr
- Removed iostream include
Fixed some lint problems
More lint problems fixed
Moved Testing code from Sample to Test.