
This is a simple demonstration of adding an import hook that verifies
a digital signature on a Python code object before allowing it to be
imported.  There are three files:

	* sign.py, which signs all the *.pyc files in the directories
listed on the command line.  The contents of the .pyc file is stored
along with the signature in a file whose name ends with .pys .

	* secimp.py, which implements a secimport() function which
will use *.pys files.  

	* testkey.py is the key used to sign and verify *.pys files.

To try it out:
	1. Run "sign.py ." to compile and sign all the *.py files in
the current directory.

	2. Run secimp.py from the command-line; it will try to
securely import testkey.pys, which should succeed.

	3. Fire up your favorite editor, and change a single byte in a
string somewhere in testkey.pys.  Run secimp.py again; it should raise
an exception when the signature can't be verified.
