Add support for binary pickles to the shelve module. In some situations

Add support for binary pickles to the shelve module.  In some situations
this can result in significantly smaller files.  All classes as well as the
open function now accept an optional binary parameter, which defaults to
False for backward compatibility.  Added a small test suite, updated the
libref documentation (including documenting the exported classes and fixing
a few other nits) and added a note about the change to Misc/NEWS.