Fixed truncation race with lock_retrieve() in lock_store().
The file has to be truncated only once the exclusive lock is held.
Removed spurious debugging messages in .xs file.
Fixed memory corruption on croaks during thaw().
Made code compile cleanly with -Wall.
Changed tagnum and classnum from I32 to IV in context.
Changes:
Fixed incorrect error message.
Now bless objects ASAP at retrieve time, which should fix two bugs.
Add support for blessed ref to tied structures (-> binary format change).
More tests.
