Session ID from Interpreter for Win32 FilePlugin

Hi Andreas,

The FilePlugin support code for Win32 should now obtain session ID from the
interpreter rather than make its own. This affects the Win32 OSProcessPlugin,
which now uses the session ID from the intepreter to make file streams for
console stdin, stdout, stderr and for OS pipe endpoints.

A patch file and a patched copy of platforms/win32/plugins/FilePlugin/sqWin32FilePrims.c
is attached. The patch is relative to SVN 1258.

Thanks,

Dave