Add VERBOSE_VCD_FILE #ifdef

This allows me to add a comment to every line emitted to the VCD file
that contains the signal's full Flo name.  This is useful for
debugging VCD dump signal naming problems, but probably shouldn't be
enabled otherwise.
Fix some VCD dump signal naming bugs

There were actually a host of bugs that could arrise from these
errors.  All of them would result in VCD signals being named wrong:
sometimes signals ended up in the wrong modules, and sometimes modules
ended up duplicated.

The DES test case that comes soon tests for these, but I figured it'd
be good to keep it seperate.
Allow for symlinked test.* files

This allows oddly-named test cases to work around the fact that the
rest of the test harness expectes everything to be named "test.*" by
symlinking stuff into place.
Run "opt" with "-O2", not "-O3"

This is faster (to run and to compile) and is probably more reliable.
Add a DES test case

This is the first large test case I've ever run.  It's definately
bigger than any of the other tests, but it doesn't actually appear to
be any more complicated -- the test pretty much just does a whole
bunch of single-bit operations.

DES does, however, provide a pretty decent test for the VCD dumper.
It found a whole bunch of bugs related to designs that actually have
more than 3 levels in their module hierarchy, which is probably a good
thing.

It's also the first test that's big enough to potientally benchmark,
which could be interesting!