Define MNT_DETACH for pid isolator.

MNT_DETACH (since Linux 2.4.11) may not be defined in older
<sys/mount.h>.

Review: https://reviews.apache.org/r/27341
Added MesosCon'14 playlist to presentations.

This closes: #27
Review: https://github.com/apache/mesos/pull/27
Allow mesos containerizer to destroy correctly at each state.