[patch] prevent burncd from failing when device is busy while trying to eject

this patch was submitted by Jaakko Heinonen in january, but didn't get
committed to HEAD yet.

when burncd is used in combination with the eject switch it doesn't care if
the device is busy or not. if eject doesn't succeed burncd fails with EIO.

the patch issues ATAPI_TEST_UNIT_READY by calling (ioctl(fd, CDIOCRESET). this
gets repeated as long as the device isn't busy anymore or a timeout is being
reached.

this patch depends upon the removal of a bogus privilege check in
sys/dev/ata/ata-cd.c

would be nice if somebody could commit both patches. they've been tested for
almost a year now and cause no breakage to occur.

they can also safely be merged to 8-stable.

in order to make it into 7- and 6-stable this other patch (bin/95979) has to
be mfc'ed to those branches first.

thanks in advance.
alex