Squashed 'src/leveldb/' changes from aca1ffc..ae6c262

ae6c262 Merge branch 'leveldb' into ripple-fork
28fa222 Looks like a bit more delay is needed to smooth the latency.
a18f3e6 Tidy up JobQueue, add ripple_core module
ab82e57 Release leveldb 1.12
02c6259 Release leveldb 1.11
5bbb544 Rate limit compactions with a 25ms pause after each complete file.
8c29c47 LevelDB issue 178 fix: cannot resize a level 0 compaction set
18b245c Added GNU/kFreeBSD kernel name (TARGET_OS)
8be9d12 CondVar::SignalAll was broken, leading to deadlocks on Windows builds. http://code.google.com/p/leveldb/issues/detail?id=149
c9fc070 Upgrade LevelDB to 1.10.0, mostly for better write stall logging.
8215b15 Tweak to variable name to support unity build

git-subtree-dir: src/leveldb
git-subtree-split: ae6c2620b2ef3d5c69e63dc0eda865d6a39fa061
Merge commit 'adae78ea9940f4d44382967d1296e7db0b54a4de' into leveldb-squashed
Merge pull request #2702 from vinniefalco/leveldb-subtree-at-1-10-0

Leveldb subtree at 1 12 0
Allow SendMessages to run partially without cs_main

SendMessages() tries to acquire a cs_main lock now, but this isn't nessecary
for much of its functionality. Move those parts out of the locked section,
so they can always be performed, and we hold cs_main for a shorter time.
Run node deletions outside of cs_vNodes
Push down cs_main locking in ProcessMessage
Improve handling of obscure reorganizations

This fixes some weird reorganization issues that probably don't normally
occur, but can be triggered when blacklisting arbitrary blocks is enabled.
Add blacklistblock RPC

As this is a fairly dangerous operation, it is normally disabled when
building. Define ENABLE_BLOCK_BLACKLISTING to enable compiling it in.
Begin headers-first synchronization
RPC updates after header-first synchronization