[PythonCAD] File saving code changes now in repo

[Art Haas]

Hi.

I've added the code the reworks the file saving routines to the
repository and sent it out. The routines use the os.rename()
function, but I've also written a routine that uses a file reading
and writing approach. The rename() approach doesn't work nicely
with hardlinks, while the second does ... but the second can
mess up files unexpectedly if the written file is a symbolic or
hardlinked file. I've used the rename() approach previously, and
by default XEmacs does the same, though XEmacs can be changed
to use a read/write routine.

There are some small code fixes in the repo as well.

-- 
Man once surrendering his reason, has no remaining guard against absurdities
the most monstrous, and like a ship without rudder, is the sport of every wind.

-Thomas Jefferson to James Smith, 1822