Switch from doing our own parsing of command line arguments to
using getopt(3) to do it.  Aside from simplifying things, this allows us to
specify multiple arguments; the old code could only accept two arguments
(input_mode and kconfig name).

Note some subtle changes:
 - The argument '-?' is no longer supported.
 - '-h' is not treated as an error, so output goes to stdout, and we
   exit with '0'.
 - There is no compatibility checking amongst arguments; the last option
   will simply override earlier options.  For example, 'conf -n -y foo'
   is perfectly valid now (input_mode will be set_yes).  Previously, that
   would have been an error ("can't find file -y").
Signed-off-by: Andres Salomon <dilinger@debian.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Roman Zippel <zippel@linux-m68k.org>