Open MPI parsing of proc mounts needs help

Open MPI tries to parse proc/mounts (not the hwloc part), which dies if entries exceed the size of the buffer used to read a line from the file.  The technique in hwloc using `setmntent` and `getmntent` to parse /proc/mounts is probably the way to go.

This problem shows up regularly on Cray XC's running CLE 6.
