acquisition.

Rearranged init to handle errors better.

overridable method.  This is needed to implement a clear method
in a subclass that allows an inverted index to be "cleared" without
actually updating data records.

Made some slight optimizations.

Got rid of get/setstate.
Made result-list-specific methods use mapping prootcol to make it
easier to mix with other mapping types.

try to avoid one-element tries by storing partial-key/value tuples
instead of sub-tries.

Fixed dealloc bug.

better error handling.

products if DateTime subclasses are mixed with ExtensionClasses.

numbers more easily.

use put2() in save_reduce() and save_inst() only if state is not a dictionary
removed put2() from save_tuple()

added cPickle_PyMapping_HasKey to replace leaking PyMapping_HasKey
lists and dictionaries are put in memo before saving their items
put2() added so that refcnt check isn't done in various cases

into object initializer, so it gets applied in all cases.