axfer: check whether a terminal is referred for stdio

axfer: check whether a terminal is referred for stdio

A reference to a terminal for standard input/output brings some
troubles. For capture transmission, it can bring some terminal
control codes and it's possible to make the terminal in disorder.
For playback transmission, it can bring endless loop to read
data for detection of type of container.

This commit checks whether a terminal is referred for the standard
input/output by a call isatty(3). When detecting a terminal,
axfer run time prints message and goes to finish.

Suggested-by: Takashi Iwai <tiwai@suse.com>
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>