pcp updates: refine dm persistent name mapping for older platforms

[Mark Goodwin <mgoodwin@xxxxxxxxxx>]

Changes committed to git://git.performancecopilot.org/markgw/pcp/pcp.git dev

commit 61b06df88fca55bed487e1d7e672760c64599e10
Author: Mark Goodwin <mgoodwin@xxxxxxxxxx>
Date:   Fri Jul 25 11:19:38 2014 +1000

    Refine the dm-* -> persistent name mapping to support older platforms.

    Older platforms (e.g. RHEL5) do not support /sys/block/dm*/dm/name
    so we have to match up the dev_t of block devices in /dev/mapper with
    their major/minor numbers in /proc/diskstats.

        modified:   src/pmdas/linux/proc_partitions.c