Fixed the cgroup isolator RSS memory reporting.

Report the number of bytes used by the memory cgroup, and stop
reporting memory with no file backed pages taken into account.

From: Eric Biederman <ebiederm@xmission.com>
Review: https://reviews.apache.org/r/14825
Fixed configure.ac to use $CC instead of 'gcc' for version checking.

This has caused problems in settings where the desired compiler
isn't the system bundled GCC (as in Mac OS X Mavericks builds where
we have been using specific versions of GCC).

Review #14164 is re-enabled for $(CC) instead of 'gcc' and lets us
compile with GCC 4.8 on Mavericks instead of down-grading to 4.7.

From: Niklas Nielsen <nik@qni.dk>
Review: https://reviews.apache.org/r/15193
Preferred ng-show to jQuery for #no-leader-alert.

Mixing jQuery DOM access with Angular creates two locations for state
storage. Always prefer Angular to jQuery for changing the DOM.

* Removed the "Close" button because the alert is not dismissable.

Review: https://reviews.apache.org/r/15154
Fixed a race condition in the Cgroups Isolator.
Removed an incorrect TODO.

Review: https://reviews.apache.org/r/15044
Fixed a pid comparison in the scheduler driver.

Review: https://reviews.apache.org/r/15065
Fixed the flaky ReconcileTasksMissingFromSlave test.

Review: https://reviews.apache.org/r/15254
Added a preliminary Committer's Guide.