ls-files: die instead of fprintf/exit in -i error

When ls-files was called with -i but no exclude pattern, it was calling fprintf(stderr, "...", NULL) and then exiting. On Solaris, passing NULL into fprintf was causing a segfault. On glibc systems, it was simply producing incorrect output (eg: "(null)": ...). The NULL pointer was a result of argv[0] not being preserved by the option parser. Instead of requesting that the option parser preserve argv[0], use die() with a constant string. A trigger for this bug was: `git ls-files -i` Signed-off-by: Ben Walton <bwalton@artsci.utoronto.ca> Signed-off-by: Junio C Hamano <gitster@pobox.com>