handle_options(): do not miscount how many arguments were used

handle_options(): do not miscount how many arguments were used

The handle_options() function advances the base of the argument array and
returns the number of arguments it used. The caller in handle_alias()
wants to reallocate the argv array it passes to this function, and
attempts to do so by subtracting the returned value to compensate for the
change handle_options() makes to the new_argv.

But handle_options() did not correctly count when "-c <config=value>" is
given, causing a wrong pointer to be passed to realloc().

Fix it by saving the original argv at the beginning of handle_options(),
and return the difference between the final value of argv, which will
relieve the places that move the array pointer from the additional burden
of keeping track of "handled" counter.

Noticed-by: Kazuki Tsujimoto
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>