rustc: Move to 'crate_name'

crate_id is being moved out of rustc (and support added to cargo).
Fix up the library and Makefile to use the new `crate_name` attribute.
Makefile: Simplify library name

Now that rustc produces predictable filenames for libraries, just code
these into the Makefile instead of querying rustc for the already
known name.
Makefile: Fix the clean target

The clean target was a remnant of the old build rules.  Replace it
with a simpler version that just removes the `target` directory.
Wrap transactions for pool

Start pool operations with a manual transaction, and commit as part of
flush.
Eliminate current warnings

Configure the transaction code for testing only, since it isn't
actually being used (move into a mod?).  Otherwise fix up a few
warnings about unused variables or dead code.