import: Use getopt_long() for parsing arguments
import: Use getopt_long() for parsing arguments

This patch converts builtin-import.c to use getopt_long() for parsing command
line arguments and cleans up error messages when opening input or output file
fails.

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@cs.helsinki.fi>

penberg/pstore,penberg/pstore,penberg/pstore,penberg/pstore