dangers of trying to iterate over weak dicts.

(Requested by Alex Martelli.)

* Improve the hash function to increase the chance that distinct sets will
  have distinct xor'd hash totals.

* Use PyDict_Merge where possible (it is faster than an equivalent iter/set
  pair).

* Don't rebuild dictionaries where the input already has one.

Also SF patch 843455.

This is a critical bugfix.
I'll backport to 2.3 maint, but not beyond that.  The bugs this fixes
have been there since weakrefs were introduced.

from the OS9 readme that is still relevant.
Got rid of Distributions/readme.txt.

Cleaned up various things in the toolbox modules.

to pymactoolbox.h (where it should have been in the first place).

MacOS9isms.

later.

pre-carbon MacOS9 support.

and the biggest in size, but probably the easiest. Hunting through the
source code comes next.

release23-maint branch:
- Remember the scroll position when rebuilding the browser (as we do far
too often). Fixes #824430.
- Allow for the documentation to be inside PythonIDE as well as in
the Python.app inside the framework (the original location for 2.3).
- Updated version numbers
- In PythonIDE, add the Tools/IDE directory as the second entry in
sys.path in stead of as the first, leaving PythonIDE.app/Contents/Resources
as the first one.
- The code for setting the working directory to $HOME was both incorrect
and in the wrong place, fixed.
- On OSX the default location for IDE scripts is now
$HOME/Library/Python/IDE-Scripts.