Assign bool directly to JSON::Value.

This change removes the workaround that was necessary now that
https://issues.apache.org/jira/browse/MESOS-939 is committed.

Review: https://reviews.apache.org/r/18540
Patched glog to compile demangle.cc with clang.

Review: https://reviews.apache.org/r/18307
Fixed compile errors in lib stout when using Clang 3.5 on Ubuntu
13.10.

Review: https://reviews.apache.org/r/18425
Fixed compile errors in mesos with Clang 3.5 on Ubuntu 13.10.

Review: https://reviews.apache.org/r/18426