gh-51 Improved Random Number Generation Performance and add Exponential distribution support (sears)

Remove synchronization points from random number generation.  This mostly consisted switching from per-class instances of Random() that are shared amongst threads to thread-local instances shared across classes.

Also, CounterGenerator.nextInt() was synchronized.  Changed it to use an AtomicInteger.

Finally, removed lastString() from Generator, as it was only called in places where lastInt() was more appropriate; switched the calls to lastInt().

We use FNV hash functions to generate a large indexable sequence of non-colliding keys.  Unforunately, for reasonably sized
workloads, this leads to key collisions, which throws off experiments.

The implementations of the FNV32 and FNV64 hash functions we use manipulate signed integers instead of unsigned integers, so it
is unclear if this is a limitation of the FNV algorithms or of our implementations.

As a workaround, this patch switches from FNV32 to FNV64, reducing the chances of such bad behavior (and eliminating it in our
experiments to date).

gh-44 Constant occupancy workload (sears)
gh-45 Modify DB API for efficient large object support (sears)

gh-45 Modify DB API for efficient large object support (sears)

 1) Add Makefile.download-db-libs, which downloads + unpacks all of the dependencies.
 2) Fix build.xml so that downloaded libraries don't break ant doc
 3) Add dbcompile-all target that builds all of the client libraries at once.

change DB API to use ByteIterator for fields instead of String.  This fixes a number of scalability problems.

NoSQL databases are capable on sub-millisecond latencies and YCSB
was only measuring times with millisecond granularity. This caused
transactions that took place in less than a second to be recorded
as taking 0 time to complete and as a result had the potential to
skew test results. This fix changes the timing granularity to
microseconds.