Allow forcing ownership even when using --rpm-use-file-permissions

The rpm-use-file-permissions setting asks each file who owns it and what
the mode is. Sometimes you only want the mode, or sometimes the user is
not correct for deployment. Now, specifying --rpm-user will force the
owner to be the given user but still respect the file modes gathered
by --rpm-use-file-permissions.

The intent of this change is:

* --rpm-use-file-permissions still works the same, when alone
* --rpm-user forces the 'user' owner regardless of the above
* --rpm-group forces the 'group' owner regardless of the above

This was identified by https://logstash.jira.com/browse/LOGSTASH-2012
Merge pull request #679 from jordansissel/fix-rpm-permissions-and-user-settings

Allow forcing ownership even when using --rpm-use-file-permissions
Add special handling for `fpm --version`

Because --version is a valid flag (for setting the package version)
but is also commonly used to ask an application what version it is,
we need a bit of special handling for `fpm --version`:

New result:

    % fpm --version
    1.1.0

Prior to this patch, `fpm --version` would tell you that you were
missing arguments or flags.