* path.cc (fs_info::update): Set and use is_cdrom.

* path.cc (fs_info::update): Set and use is_cdrom.
* path.cc (fillout_mntent): Set ret.mnt_type to something more Linux-like,
based on data from fs_info.  Move "system" and "user" strings from mnt_type to
mnt_opts.
* path.h (struct fs_info): Add is_cdrom field.
* path.h (fs_info::clear): Initialize is_cdrom.
* path.h (struct fs_info): Add IMPLEMENT_STATUS_FLAG(bool,is_cdrom).
* path.h (class path_conv): Add fs_is_cdrom method.  Add missing fs_is_netapp
method.