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