Suppress clang warnings when compiling bundled boost 1.56

Clang generates a bunch of warnings of the type:
bundled/boost-1.56.0/include/boost/preprocessor/tuple/eat.hpp:23:26: warning: variadic macros are a C99 feature [-Wvariadic-macros]
bundled/boost-1.56.0/include/boost/mpl/if.hpp:131:1: warning: empty macro arguments are a C99 feature [-Wc99-extensions]

This patch just disables those warnings. Also see https://code.google.com/p/dealii/issues/detail?id=252
Merge pull request #121 from tjhei/clang_boost_warnings

Suppress clang warnings when compiling bundled boost 1.56
Replace all occurrences of std_cxx1x by std_cxx11.

Keep the old files and namespace for backward compatibility.
Replace all occurrences of std_cxx1x by std_cxx11 also in tests/.
Merge pull request #111 from bangerth/replace-std_cxx1x-by-std_cxx11

Replace all occurrences of std_cxx1x by std_cxx11.
Replace the original attempt at providing step-53 by something real.

In particular, provide a step-53 that shows how to describe geometries
using charts and use a section of Earth under Eastern Africa as an
example. This has about the right level of complexity, and produces
awesome pictures.

This commit was generated from a number of smaller one:

More text.

Implement the Africa model for the WGS 84 geometry (actual topography still missing).

Provide the actual data set. Provide a way of reading it when not compressed.

Results and finish the program. Much still to be done.

More text.

Finish documenting everything.

Remove a picture we now no longer need.
Provide some cross-references to the new step-53.
Show some more results.
Downsample the data file by a factor of 3 in each direction. Adjust the program accordingly.
Add a changelog entry.
Clarify where the data comes from.