A number of smaller fixes and performance improvements:

- Implemented Get() directly instead of building on top of a full
  merging iterator stack.  This speeds up the "readrandom" benchmark
  by up to 15-30%.

- Fixed an opensource compilation problem.
  Added --db=<name> flag to control where the database is placed.

- Automatically compact a file when we have done enough
  overlapping seeks to that file.

- Fixed a performance bug where we would read from at least one
  file in a level even if none of the files overlapped the key
  being read.

- Makefile fix for Mac OSX installations that have XCode 4 without XCode 3.

- Unified the two occurrences of binary search in a file-list
  into one routine.

- Found and fixed a bug where we would unnecessarily search the
  last file when looking for a key larger than all data in the
  level.

- A fix to avoid the need for trivial move compactions and
  therefore gets rid of two out of five syncs in "fillseq".

- Removed the MANIFEST file write when switching to a new
  memtable/log-file for a 10-20% improvement on fill speed on ext4.

- Adding a SNAPPY setting in the Makefile for folks who have
  Snappy installed. Snappy compresses values and speeds up writes.



git-svn-id: https://leveldb.googlecode.com/svn/trunk@32 62dab493-f737-651d-591e-8d6aee1b9529

TODO

@@ -8,7 +8,6 @@ db
   object stores, etc. can be done in the background anyway, so
   probably not that important.
 
-api changes:
-- Make it wrappable
-
-Faster Get implementation
+After a range is completely deleted, what gets rid of the
+corresponding files if we do no future changes to that range.  Make
+the conditions for triggering compactions fire in more situations?