Fix busy detection of file systems inside Linux Software RAID (#712533)

On some distributions GParted doesn't detect when a file system is busy
and mounted when the partition is within a Linux Software RAID array.
Affected distributions include: Debian 6, Debian 7 and RHEL/CentOS 6.x.

This is because of a bug in libparted 2.3 and earlier.  It was fixed by
this change in libparted 2.4:
    http://git.savannah.gnu.org/cgit/parted.git/commit/?id=db52898c214310dab4ed84e6cb2f9ffc8c3aa502
    linux: also detect "in-use" dmraid and scsi-Nth (N>=16) partition

Ubuntu 13.10 with libparted 2.3 is not affected because it contains a
distribution specific patch to correct it.

Fix by using GParted's internal mounted partitions map, mount_info, to
determine if a partition is busy, in addition to using libparted's
ped_partition_is_busy().

Bug #712533 - Partitions not detected as busy inside Software RAID on
              some distros