Fix compile issue in Mac OS

Summary:
Compile issues are:
* Unused variable env_
* Unused fallocate_with_keep_size_

Test Plan: compiles

Reviewers: dhruba, haobo, sdong

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17043
add tags to gitignore
Don't compact with zero input files

Summary:
We have an issue with internal service trying to run compaction with zero input files:
2014/02/07-02:26:58.386531 7f79117ec700 Compaction start summary: Base version 1420 Base level 3, seek compaction:0, inputs:[ϛ~^Qy^?],[]
2014/02/07-02:26:58.386539 7f79117ec700 Compacted 0@3 + 0@4 files => 0 bytes

There are two issues:
* inputsummary is printing out junk
* it's constantly retrying (since I guess madeProgress is true), so it prints out a lot of data in the LOG file (40GB in one day).

I read through the Level compaction picker and added some failure condition if input[0] is empty. I think PickCompaction() should not return compaction with zero input files with this change. I'm not confident enough to add an assertion though :)

Test Plan: make check

Reviewers: dhruba, haobo, sdong, kailiu

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16005
Fix two bugs in talbe format

Summary:
Previous code had two bugs:

* didn't initialize the table_magic_number_ explicitly -- as a
  result a random junk number is stored for table_magic_number_, making
  HasInitializedMagicNumber() always return true.
* if condition is inconrrect in set_table_magic_number(), and the return value is not checked.
  I replace if-else by a stronger requirement enforced by assert().

Test Plan:
Previous sst_dump failed to work.
After the fix, things back to normal.

Reviewers: yhchiang

CC: haobo, sdong, igor, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D17055
ComputeCompactionScore in CompactionPicker

Summary:
As it turns out, we need the call to ComputeCompactionScore (previously: Finalize) in CompactionPicker.

The issue caused a deadlock in db_stress: http://ci-builds.fb.com/job/rocksdb_crashtest/290/console

The last two lines before a deadlock were:
2014/03/18-22:43:41.481029 7facafbee700 (Original Log Time 2014/03/18-22:43:41.480989) Compaction nothing to do
2014/03/18-22:43:41.481041 7faccf7fc700 wait for fewer level0 files...

"Compaction nothing to do" and other thread waiting for fewer level0 files. Hm hm.

I moved the pre-sorting to SaveTo, which should fix both the original and the new issue.

Test Plan: make check for now, will run db_stress in jenkins

Reviewers: dhruba, haobo, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17037
Add a unit test to verify compaction filter context

Summary: Add unit tests to make sure CompactionFilterContext::is_manual_compaction_ and CompactionFilterContext::is_full_compaction_ are set correctly.

Test Plan: run the new tests.

Reviewers: haobo, igor, dhruba, yhchiang, ljin

Reviewed By: haobo

CC: nkg-, leveldb

Differential Revision: https://reviews.facebook.net/D17067
Fix DBTest.UniversalCompactionTrigger failure caused by D17067

Summary: D17067 breaks DBTest.UniversalCompactionTrigger because of wrong location of the checking. Fix it.

Test Plan: Run the test and make sure it passes.

Reviewers: igor, haobo

Reviewed By: igor

CC: dhruba, ljin, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D17079
Delete rocksdb dir after crashtest

Summary:
We should clean up after ourselves. Last crashtest failed because the disk on the cibuild machine was full.

Also, db_crashtest is supposed to run the test on the same database in every iteration. This isn't the case currently, because every run creates a new tmp directory. It's fixed with this diff.

Test Plan: ran it

Reviewers: ljin

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17073
If paranoid_checks -- Mark DB read-only on any IOError

Summary:
Whenever we get an IOError from GetImpl() or NewIterator(), we should immediatelly mark the DB read-only. The same check already exists in Write() and Compaction().

This should help with clients that are somehow missing a file.

Test Plan: make check

Reviewers: dhruba, haobo, sdong, ljin

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17061
Consistency Check Function

Summary: Added a function/command to check the consistency of live files' meta data

Test Plan:
Manual test (size mismatch, file not exist).
Command test script.

Reviewers: haobo

Reviewed By: haobo

CC: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D16935