Use valgrind's "--log-file" option

The new libflo outputs some warnings based on workarounds for a Chisel
bug.  This causes the valgrind tests to get confused, as they parse
stderr.

Luckily we can instead simply use valgrind's "--log-file" option,
which re-routes valgrind's output to a file instead.
Use a for loop to initialize memories

I guess I made the same mistake Donggyu made... :)
Implement DIV

There's no test for this, so you'll just have to trust me...  The test
is in chisel-torture, which explicitly doesn't test for
divide-by-zero.
Implement ARSH

This is pretty simple: it's just a slight change to RSH that outputs
the arithmatic version to LLVM.
Implement LOG2

There's a test for this one.  Note that the current implementation is
pretty horrible (it uses an unrolled loop), but it's the best I can
come up with because LLVM doesn't appear to have a log2 intrinsic
(well, I could probably write a tighter loop, but who cares).

I'd consider the lack of a log2 intrinsic an LLVM bug...
Bump version to 0.0.13