db_bench: seekrandom can specify --seek_nexts to read specific keys after seek.

Summary:
Add a function as tittle.
Also use the same parameter to fillseekseq too.

Test Plan: Run seekrandom using the new parameter

Reviewers: ljin, MarkCallaghan

Reviewed By: MarkCallaghan

Subscribers: rven, igor, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D25035
Ignore IntelliJ idea project files and ignore java/out folder
Feature - Implement Java API for Comparator and Slice. Allows use of
either byte[] or DirectByteBuffer for accessing underlying data.
Add locking to comparator jni callback methods which must be thread-safe
Fix to memory dealocation when creating a slice from a byte buffer
Fix code style problems identified by lint
Tests for ComparatorOptions, Comparator and DirectComparator, and by
proxy we also exercise Slice and DirectSlice
Fix code review comments raised in https://reviews.facebook.net/D22779
Merge pull request #231 from adamretter/master

Java API for Comparator and Slice
Fix DeleteFile() + enable deleting files oldest files in level 0

Summary:
DeleteFile() call was broken for non-default column family. This fixes it. We might need this feature for mongo.

I also introduced a possibility of deleting oldest file in level 0.

Test Plan: added unit test to deletefile_test

Reviewers: ljin, yhchiang, rven, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D24909
BlockBasedTableConfig & PlainTableConfig enhancements

BlockBasedTableConfig
- ported Checksum
- ported IndexType

PlainTableConfig
- added missing options
- added EncodingType