am: don't pass strvec to apply_parse_options()

am: don't pass strvec to apply_parse_options()

apply_parse_options() passes the array of argument strings to
parse_options(), which removes recognized options.  The removed strings
are not freed, though.

Make a copy of the strvec to pass to the function to retain the pointers
of its strings, so we release them all at the end.

Signed-off-by: René Scharfe <redacted>
Signed-off-by: Junio C Hamano <redacted>