Ignored the recovery error due to the inability to
find the latest executor run.

Review: https://reviews.apache.org/r/14001
Update Powered By page to reflect new organizations using Mesos.
Adds new documentation page to include links to videos and slides for Mesos presentations.
Fixed the broken OsTest.process and OsTest.killtree tests.

Review: https://reviews.apache.org/r/14072
Hid links to dead slaves to prevent dead links.

If a slave is gone, the framework page will print "Slave gone" in place
of the links to the slave's UI. The links would previously fail in
redirection and return the user to the Mesos root page, which is
unpleasant.

Fixes: https://issues.apache.org/jira/browse/MESOS-650

Review: http://reviews.apache.org/r/14074
Removes 90 day plan from documentation, which is no longer relevant.
Updates formatting of heads on Mesos presentations documentation.
Cleaned up some log and CHECK messages.

Review: https://reviews.apache.org/r/14135
Fixed broken build on GCC 4.8 due to -Wall.

With GCC 4.8, Boost fails to build from '-Wunused-local-typedefs', which
is implied by '-Wall'.

Review: https://reviews.apache.org/r/11974/