Only darwin/clang needs GTEST to supply its own tr1 tuple.

Review: https://reviews.apache.org/r/19077
Switched to cxx11 by default for libprocess.

Review: https://reviews.apache.org/r/18577
Switched to cxx11 by default for mesos.

Review: https://reviews.apache.org/r/18576
Fixed fetcher to properly fetch multiple URIs.

Review: https://reviews.apache.org/r/18974
Added test for subprocess with environment variable set.

Review: https://reviews.apache.org/r/19144
Updated CHANGELOG for 0.18.0-rc4.
Removal of python-boto from the repo and add configure checks.

Python boto exists on nearly all platforms that I can think of. It
makes sense to add the check to configure and remove from the repo.

Review: https://reviews.apache.org/r/18910
Fixed the path to 'mesos-master' in configuration.md.
Fixed missing inline for cleanup.

Review: https://reviews.apache.org/r/19214
Changed Option::get to return a const reference to reduce copying.

Review: https://reviews.apache.org/r/18383
Option::get reference cleanup in libprocess.

Review: https://reviews.apache.org/r/18384
Option::get reference cleanup in mesos.

Review: https://reviews.apache.org/r/18386
Fixed build failure of Python-Egg on OS X and clang 3.4.

Workaround for incompatibility of clang 3.4 with build settings of
Apple's Python distribution. Adds PYTHON_CFLAGS and PYTHON_CPPFLAGS to
configuration phase. Those variables are pre-populated by the contents
of CFLAGS and CPPFLAGS. When clang is used for the compilation, the
-Qunused-arguments override is added to both variables to deescalate
possible errors caused by unknown commandline flags towards warnings,
thus allowing to build our Python egg with clang 3.4 (Xcode 5.1) and
Apple's default Python.

Review: https://reviews.apache.org/r/19068
Display warning for credentials file permissions.

Review: https://reviews.apache.org/r/19093
Changed cpu shares from size_t to uint64_t.

Review: https://reviews.apache.org/r/18966
Added tests for InMemoryStorage.

Review: https://reviews.apache.org/r/19072
Added a --registry_strict_operations flag that must be false for now.

Review: https://reviews.apache.org/r/19135
Implemented optional strictness in the Registrar.

Review: https://reviews.apache.org/r/19085
Switched from LevelDBStorage to InMemoryStorage for registry flag.

Review: https://reviews.apache.org/r/19134
Added structs for Slaves and Frameworks in the Master.

Review: https://reviews.apache.org/r/19166