isatty() doesn't return zero for named pipe handle

[guest]

From froloff

isatty() function return wrong value for named pipe handle, which was inherited from parent process.

It works fine for unnamed pipe handles.

I didn't test isatty() behavior, if named pipe created inside the process calling this function.

Tested with libc063 version.

[bird]

(In [3728]) testcase for the alleged isatty bug. References #197.