Deprecated use of MESOS_NATIVE_LIBRARY for JVM frameworks.

Introduced a new environment variable, MESOS_NATIVE_JAVA_LIBRARY. That
variable still points towards libmesos. For allowing a smooth
transition away from MESOS_NATIVE_LIBRARY towards
MESOS_NATIVE_JAVA_LIBRARY whithin JVM based frameworks.

Future versions of MESOS_NATIVE_LIBRARY will not point to valid JNI
bindings.

A typical java-based framework relies on mesos.jar to do the loading
but may use some extra logic in its startup to make sure
MESOS_NATIVE[_JAVA]_LIBRARY is set/valid. That extra-logic should now
be adapted by the framework developers to use the new environment
variable instead of the old one.  MESOS_NATIVE_LIBRARY is now marked
as being deprecated for use for JVM based frameworks.

Note: MESOS_NATIVE_LIRBRAY will not be removed. It is kept for
frameworks that are not JVM based but need to bind to the
self-contained Mesos library.

Review: https://reviews.apache.org/r/19117
Replaced Try::error with Error in master detector.

Review: https://reviews.apache.org/r/19299
Adds Atlassian to Powered By Mesos list.
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