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
[RocksJava] Options Refactoring 3.6

Summary:
Preparational pull request. The main point about these changes is
to enable RocksJava in a next step to provide custom ColumnFamilyOptions.
DBOptions and ColumnFamilyOptions are now available as well as Interfaces
which describe those methods.

Methods in interfaces and class definitions of DBOptions and ColumnFamilyOptions
are ordered according to C++ implementation.

Optimize methods were ported to Java. (OptimizeForPointLookup,
OptimizeLevelCompaction, OptimizeUniversalCompaction).

To align BuiltinComparator with every other Enum it was moved to
a separate file.

A new test was introduced which includes some basic testing of
ColumnFamilyOptions and DBOptions.

Note: The changes are fully downwards compatible.

Test Plan:
make rocksdbjava
make jtest

Differential Revision: https://reviews.facebook.net/D25203