Address minor compiler warnings.

Zap a couple unused vars.  Add a cast.
Add dump() and load() to Freezer.
Use Freezer instead of Dump/Load.

Instead of invoking Dump/Load methods on Obj, Hash and VArray object,
use Freezer_dump and Freezer_load.
Remove VTable_Load_Obj.

VTable_Load_Obj is an inefficiently implemented convenience method.  Zap
it.
Update test for `nullable` to avoid Dump().

Change the test for the behavior of Perl wrappers around `nullable`
return values to use Inc_RefCount() instead of Dump().
Finish moving Dump/Load from Clownfish to Lucy.

Remove Dump/Load methods from the Clownfish runtime and move their
binding specs up into the Lucy classes that need them.
Fix minor compiler warnings.

Remove unused function, add a couple casts.

This commit hould be folded into other commits before merging to master.