samples: rework show-tuple

Now that we are using defconfig files, the samples do not contain
the full configuration, so we can not simply parse them to show
their content.

Instead, we must fake recalling a sample, and parse the generated
.config file.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

This is NOT the official version of dialog.  This version has been

significantly modified from the original.  It is for use by the Linux

kernel configuration script.  Please do not bother Savio Lam with 

questions about this program.