various platforms; improve android port speed.

Avoid static initializer by using a new portability interface for
thread-safe lazy initialization.  Custom ports will need to be
extended to implement InitOnce/OnceType/LEVELDB_ONCE_INIT.

Fix endian-ness detection (fixes Powerpc builds).

Build related fixes:
- Support platforms that have unversioned shared libraries.
- Fix IOS build rules.

Android improvements
- Speed up atomic pointers
- Share more code with port_posix.

Do not spin in a tight loop attempting compactions if the file system
is inaccessible (e.g., if kerberos tickets have expired or if it is out
of space).

- Replace raw slice comparison with a call to user comparator.
  Added test for custom comparators.

- Fix end of namespace comments.

- Fixed bug in picking inputs for a level-0 compaction.

  When finding overlapping files, the covered range may expand
  as files are added to the input set.  We now correctly expand
  the range when this happens instead of continuing to use the
  old range.  For example, suppose L0 contains files with the
  following ranges:

      F1: a .. d
      F2:    c .. g
      F3:       f .. j

  and the initial compaction target is F3.  We used to search
  for range f..j which yielded {F2,F3}.  However we now expand
  the range as soon as another file is added.  In this case,
  when F2 is added, we expand the range to c..j and restart the
  search.  That picks up file F1 as well.

  This change fixes a bug related to deleted keys showing up
  incorrectly after a compaction as described in Issue 44.

(Sync with upstream @25072954)

- Added a C binding for LevelDB.
  May be useful as a stable ABI that can be used by 
  programs that keep leveldb in a shared library, 
  or for JNI API.

- Replaced SQLite's readseq benchmark to a more efficient version. 
  SQLite readseq speeds increased by about a factor of 2x 
  from the previous version. Also updated benchmark page to
  reflect readseq speed up.



git-svn-id: https://leveldb.googlecode.com/svn/trunk@46 62dab493-f737-651d-591e-8d6aee1b9529

- Based on suggestions on the sqlite-users mailing list,
  we removed the superfluous index on the primary key 
  for SQLite's benchmarks, and turned write-ahead logging 
  ("WAL") on. This led to performance improvements for SQLite.

- Based on a suggestion by Florian Weimer on the leveldb
  mailing list, we disabled hard drive write-caching via
  hdparm when testing synchronous writes. This led to
  performance losses for LevelDB and Kyoto TreeDB.

- Fixed a mistake in 2.A.->Random where the bar sizes
  were switched for Kyoto TreeDB and SQLite.



git-svn-id: https://leveldb.googlecode.com/svn/trunk@45 62dab493-f737-651d-591e-8d6aee1b9529

- LevelDB patch for FreeBSD. This resolves Issue 22.
  Contributed by dforsythe (thanks!).

- Removing Chromium-specific files.
  They are now going to live in the Chromium repository.

- Adding a benchmark page comparing LevelDB performance
  to SQLite and Kyoto Cabinet's TreeDB, along with
  code to generate the benchmarks.
  Thanks to Kevin Tseng for compiling the benchmarks,
  and Scott Hess and Mikio Hirabayashi for their
  help and advice.



git-svn-id: https://leveldb.googlecode.com/svn/trunk@40 62dab493-f737-651d-591e-8d6aee1b9529