Renamed cache to Cache.

Review: https://reviews.apache.org/r/19437
Force disable C++11 in libprocess for g++-4.7.

Review: https://reviews.apache.org/r/19335
Force disable C++11 in mesos for g++-4.7.

Review: https://reviews.apache.org/r/19336
Fixed a regression in the Master stats.json endpoint.

Review: https://reviews.apache.org/r/19493
Only use 50% of the memory for systems with less than 2GB of memory.

Review: https://reviews.apache.org/r/19312
Filter all message events in the Master when not elected.

Review: https://reviews.apache.org/r/19374
Added cache::erase and cache::size.

Review: https://reviews.apache.org/r/19375
Update slave to use 50% of the disk space for machines with
fewer than 10GB of disk space.

Review: https://reviews.apache.org/r/19427
Fixed the format of DateUtils::currentDate().

Review: https://reviews.apache.org/r/19538
Changed review bot trigger to include dependency changes.

Review: https://reviews.apache.org/r/19480
Refactored the Registrar to push the operations to the callers.

Review: https://reviews.apache.org/r/19372
Changed tabs to spaces in master.cpp.
Fixed a bug to properly re-register an authenticating framework.

Review: https://reviews.apache.org/r/19542
Added support for specifying logging level via flag.

minloglevel flag is passed as an argument to the command line and it
configures the level of logging to stderr and file. It can take INFO,
WARNING, ERROR or FATAL values. All log messages at or above the
configured log level will be printed.

If 'quiet' flag is also passed to the command line, minloglevel will
affect just the logs from file (if configured by log_dir flag)

Review: https://reviews.apache.org/r/19357
MESOS-610: Split slave specific tests out of master_tests.

Review: https://reviews.apache.org/r/18752
Added tests for Cache.

Review: https://reviews.apache.org/r/19501
Implemented the Registry-backed Master.

Review: https://reviews.apache.org/r/19383
Added utility functions in stout to return MAC addresses.

Review: https://reviews.apache.org/r/19556
Added utility functions to get IPv4 address of a given link device.

Review: https://reviews.apache.org/r/19602
Fixed MESOS-1055: explicit single-argument constructors.

Put "explicit" in front of all single-argument constructors in C++
Mesos source code. (Omitted lib process, filed a separate issue for
it.)

Review: https://reviews.apache.org/r/18823