#37 async bug with py-execute-region

[David Goodger]

python-mode.el revision 4.78, GNU Emacs 21.3.1
(i386-mingw-nt5.1.2600) of 2004-03-10 (NTEmacs), Cygwin.

When executing py-execute-region with the optional
async parameter set, I get the following bug:

let*: Wrong type argument: stringp, cpython

I traced the problem to line 1749:

(start-process py-which-bufname buf shell arg file)

The "shell" variable evaluates to a symbol, 'cpython,
but start-process is expecting a string. Hard-coding
the string "python" fixes the immediate problem for me.