script: fix backward compatibility for options after non-option args

script: fix backward compatibility for options after non-option args

The commit 7268e79b added "+" to the getopt_long() options string to
support the "--" separator for specifying commands. The "+" prefix
makes getopt stop processing at the first non-option argument, which
breaks the traditional "script file -c command" usage.

Fix this by pre-scanning argv for "--" before getopt, separating the
command arguments, and removing the "+" prefix to restore GNU getopt
argument permutation.

Addresses: 7268e79bc5365034a6e5b38ac5d9bf635e2dafc2
Reported-by: Chris Hofstaedtler <zeha@debian.org>
Signed-off-by: Karel Zak <kzak@redhat.com>