Remove the loops that close all open fds before running a

Remove the loops that close all open fds before running a
subprocess. They were intended to make sure the child process didn't
inherit anything embarrassing or inconvenient from us, such as the
master end of its own pty, but now we instead do this by making sure
to set all our own fds to not-FD_CLOEXEC on creation. This should
fix Debian bug #357520.

(This doesn't seem to work _quite_ right in uxproxy.c's invocation
of a local proxy command: both ends of a GTK internal pipe end up in
the child process's fd space. This appears to be another GTK 1 bug,
inasmuch as it goes away when I build with Colin's preliminary GTK 2
patch; for the moment I think leaving that pipe lying around is
probably less harmful than hampering the proxy process's ability to
use extra fds by prior arrangement with PuTTY's parent process.)

[originally from svn r7107]