problem sourcing GDB script in interactive-mode on

problem sourcing GDB script in interactive-mode on

When interactive-mode is not auto, GDB always uses that setting to
determine whether to act as if the input stream is a terminal or not.
However, this setting should only be honored if the input stream is
the standard input stream.  Otherwise, we run into trouble while
source-ing a GDB script, as shown below (on x86_64-linux):

        % cat script
        print 1
        print 2
        % gdb  -q
        (gdb) set interactive-mode on
        (gdb) source script
        (gdb) print 3
        $1 = 3

The lack of output and the fact that the "print 3" command returned
a value saved in $1 (as opposed to $3) indicates that the script was
not even evaluated at all.

gdb/ChangeLog:

        * top.c (input_from_terminal_p): Restrict the use of interactive_mode
        to the case where instream is stdin.

gdb/testsuite/ChangeLog:

        * gdb.base/interact.exp: New testcase.