misc.file_open(): avoid traversing up real paths
misc.file_open(): avoid traversing up real paths

Unlike most of you, I use openerp on a real Linux machine. There, I still
use nfs, which would automount the /net and /home paths. The
tools.misc.file_open() algorithm would try to go up until a module structure
is found at that path.
Problem is, it may go too far up the path, testing for path+'.zip'.
Eg. for /home/panos/build/openerp/addons/... it would end up looking
for "/home/panos.zip". That's bad. Automounter would block trying to
timeout on some non-existing resource.

The previous 'isfile()' check was flawed. It usually is a dir, so
I'd better check for /any/ real path to stop the traversal.

xrg/openerp-server,xrg/openerp-server