Add getLogFile() method that provides hook for SpreadLog subclass.

This change includes a minor change to semantics for
reinitialization().

There are three chief performance-related changes:

    - Do not check whether logging is enabled in the actual log call.
      Instead check enviroment variables when the module is imported
      and whenever an explicit initialize() call is made.

      This might seem like it limits the user's ability to turn
      logging on and off, but I don't believe it does.  Logging is
      controlled by environment variables.  Once the Python script is
      working, the environment variables won't change.

      This change makes the case of no logging fast, instead of slow.

    - Each log call goes through a method on the stupid_log_write()
      object instead of through __call__().  It's much faster to call
      a method than an instance.

    - Use "print >> file" rather than "file.write()".  It appears to
      be a bit faster.

Replaced _set_stupid_dest() with _set_log_dest().

Also, reformat code using guidlines from the Friends of Whitespace.

Fix newTimeStamp() so that it always returns a timestamp.
XXX still not sure that it works.

Replace long multiplies with long shifts in U64() and u64().

    - use update() method where appropriate
    - don't pass None as second argument to get(). it's the default.
    - consistent space after comma between args

In tpc_vote() rename local variable id to tid.

Add doc string to read_index(), helpful but not complete yet.

In read_index(), replace an iteration over the tindex for each
transaction with a few calls that do the work with much less
overhead.

Also, add an open() method to open the storage.  Used by
PersistentStorage, too.

Raise correct exceptions in abortVersion() and commitVersion().

Spread out some code that had the vertical white space removed.

Fix the versions() implementation so that it works if the optional max
argument is not passed by the caller.

Fix commitVersion() so that it works for committing from one version
to the other.  The previous version always committed to the
non-version data even if a destination version was specified.

Fix typos.

documented exceptions.

Remove a few of the old #JF# comments that explain why some old,
commented out test code didn't work.  XXX still need to do more.

Extend a few tests with more checks of accessing non-version data via
versions that have no changes in them.

Comment -> doc string.

It's possible for a storage to not support historical revisions, in
which case this test can't work.

Also make comment at top of BasicStorage into a doc string.

Replace a string-based exception (a string literal which was broken
even for string-based exceptions) with a class-based exception.

Raise a VersionCommitError is source and dest versions were the same.

way all the other MinPO objects are created.  But, be sure to pass
already_pickled=1 to _dostore().

of two objects.  This uncovered a bug in Berkeley's CommitLog, which
was caused by an inadvertently committed change.

Changed the conflict resolution machinery to avoid attempting to resolve conflicts on ZClasses, because we can't import their "modules" (we don't have a db connection).

actual work

database file not to be truncated when it should have been during a
two-phase commit abort.

Simplify santiy checking of length fields in transaction metadata.
Replace the following test:
[1]    if ul > tl or dl > tl or el > tl or tl < (23+ul+dl+el):
with this one:
[2]    if tl < (23+ul+dl+el):

If any of the first three comparisons in [1] is true, then the final
test must also be true.  It's unlikely that any of the tests will be
true, so just do the final one.

This test wasn't part of read_index(), but seems good and cheap.

XXX Needs test case.