Make arena use hugepage if possible

Summary:
arena doesn't use huge page by default. This change will make it happen
if possible. A new paramerter is added for Arena(). If it's set, Arena
will use huge page always. If huge page allocation fails, Arena
allocation will fallback to malloc().

Test Plan:
Change util/arena_test to support huge page allocation.
Run below tests:
1. normal regression test:
  make check
2. Check if huge page allocation works
  echo 50 > /proc/sys/vm/nr_hugepages
  make check

Reviewers: sdong

Reviewed By: sdong

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D28647
[RocksJava] Makefile correction

Prevent non exist error message while executing
clean twice.
Fix leak when create_missing_column_families=true on ThreadStatus

Summary:
An entry of ConstantColumnFamilyInfo is created when:
1. DB::Open
2. CreateColumnFamily.

However, there are cases that DB::Open could also call CreateColumnFamily
when create_missing_column_families=true.  As a result, it will create
duplicate ConstantColumnFamilyInfo and one of them would be leaked.

Test Plan: ./deletefile_test

Reviewers: igor, sdong, ljin

Reviewed By: ljin

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D29307
Merge pull request #415 from fyrz/RocksJava-Makefile

[RocksJava] Makefile correction
Fixes valgrind error in GetSnapshotLink. Free checkpoint now.

Summary: Free checkpoint after its directory is removed.

Test Plan: Run valgrind with GetSnapshotLink.

Reviewers: igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D29493