New version, with contributions from Sjoerd Mullender and Mark Hammond.

Sjoerd writes:

This version of freeze creates one file per Python module, instead of
one humongous file for all Python modules.
bkfile: new module to used to write files with backups.  No new file
is produced if the new contents is identical to the old.
New option "-x excluded-module" for modulefinder test program.
New option "-i filename" for freeze main program to include a list of
options in place of the -i option.