Fix valgrind error caused by FileMetaData as two level iterator's index block handle

Summary: It is a regression valgrind bug caused by using FileMetaData as index block handle. One of the fields of FileMetaData is not initialized after being contructed and copied, but I'm not able to find which one. Also, I realized that it's not a good idea to use FileMetaData as in TwoLevelIterator::InitDataBlock(), a copied FileMetaData can be compared with the one in version set byte by byte, but the refs can be changed. Also comparing such a large structure is slightly more expensive. Use a simpler structure instead

Test Plan:
Run the failing valgrind test (Harness.RandomizedLongDB)
make all check

Reviewers: igor, haobo, ljin

Reviewed By: igor

CC: yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D17409
Compaction Filter V1 to use old context struct to keep backward compatible

Summary: The previous change D15087 changed existing compaction filter, which makes the commonly used class not backward compatible. Revert the older interface. Use a new interface for V2 instead.

Test Plan: make all check

Reviewers: haobo, yhchiang, igor

CC: danguo, dhruba, ljin, igor, leveldb

Differential Revision: https://reviews.facebook.net/D17223
crc32: build a whole special Extend function for SSE 4.2.

Disassembling the Extend function shows something that looks
much more healthy now. The SSE 4.2 instructions are right
there in the body of the function.

Intel(R) Core(TM) i7-3540M CPU @ 3.00GHz

Before:

crc32c: 1.305 micros/op 766260 ops/sec; 2993.2 MB/s (4K per op)

After:

crc32c: 0.442 micros/op 2263843 ops/sec; 8843.1 MB/s (4K per op)
Merge pull request #107 from alberts/fastah

crc32: build a whole special Extend function for SSE 4.2.
Move a info logging out of DB Mutex

Summary: As we know, logging can be slow, or even hang for some file systems. Move one more logging out of DB mutex.

Test Plan: make all check

Reviewers: haobo, igor, ljin

Reviewed By: igor

CC: yhchiang, nkg-, leveldb

Differential Revision: https://reviews.facebook.net/D17427
Fix valgrind error in c_test
Merge branch 'master' into jni