Support for LZ4 compression.
Merge pull request #74 from alberts/lz4

Support for LZ4 compression.
Quick fix for table_test failure

Summary:
* Fixed the compression state array size bug.
* Temporarily disable running `DoCompressionTest()` against bzip, which will fail the test.

Test Plan: make && ./table_test

Reviewers: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16065
Add LIBRARY back to `make dbg`
Reduce malloc of iterators in Get() code paths

Summary:
This patch optimized Get() code paths by avoiding malloc of iterators. Iterator creation is moved to mem table rep implementations, where a callback is called when any key is found. This is the same practice as what we do in (SST) table readers.

db_bench result for readrandom following a writeseq, with no compression, single thread and tmpfs, we see throughput improved to 144958 from 139027, about 3%.

Test Plan: make all check

Reviewers: dhruba, haobo, igor

Reviewed By: haobo

CC: leveldb, yhchiang

Differential Revision: https://reviews.facebook.net/D14685
Fix a member variables initialization order issue

Summary:
In MacOS, I got issue with `Footer`'s default constructor, which initialized the magic number with some random number instead of 0.
With investigation, I found we forgot to make the kInvalidTableMagicNumber to be static. As a result, kInvalidTableMagicNumber was assgined to `table_magic_number_` before it is initialized (which will be populated with random number).

Test Plan: passed current unit tests; also passed the unit tests for the incoming diff which used the default footer.

Reviewers: yhchiang

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16077