Make DB::Open fail if sst files are missing.

Also, cleanup for Clang's -Wimplicit-fallthrough warning.
Release leveldb 1.10

Fixes issues
147 - thanks feniksgordonfreeman
153
156
166

Additionally,
* Remove calls to exit(1).
* Fix unused-variable warnings from clang.
* Fix possible overflow error related to num_restart value >= (2^32/4).
* Add leveldbutil to .gitignore.
* Add better log messages when Write is stalled on a compaction.
Release leveldb 1.11

Fixes issues
161
174
178

As well as the issue reported by edouarda14@gmail.com about
MissingSSTFile unit test failing on windows.
Release leveldb 1.12

Non-functional changes only:
1) Add Kevin Regan to the AUTHORS file
2) Add standard license header to issues/issue178_test.cc
LevelDB 1.13

Fix issues 77, 87, 182, 190.

Additionally, fix the bug described in
https://groups.google.com/d/msg/leveldb/yL6h1mAOc20/vLU64RylIdMJ
where a large contiguous keyspace of deleted data was not getting
compacted.

Also fix a bug where options.max_open_files was not getting clamped
properly.
Merge remote-tracking branch 'google/master'

* google/master:
  LevelDB 1.13
  Release leveldb 1.12
  Release leveldb 1.11
  Release leveldb 1.10
  Make DB::Open fail if sst files are missing.

Conflicts:
	.gitignore