Fix up a few places that accidentally didn't get changed when downsampling data.
Reference the correct picture.
Fix language.
Merge pull request #130 from bangerth/fix-up-step-53-2

Fix up step 53. This was supposed to be addressed by #127 but the merge of that issue apparently encountered some problems. Here's a respin.
Move a couple of entries in the changelog to their correct place.
Merge pull request #131 from bangerth/sort-changelog

A couple of entries had ended up in the wrong place (general changes instead of specific changes). While it's debatable where exactly the line is, these items should probably be in the second category. Move them there.
Bugfix: step-53 requires enabled DEAL_II_WITH_ZLIB

step-53 uses boost's <iostreams/filter/gzip.hpp> in order to unpack the
file topography.txt.gz.

If the internal boost variant is used this requires external linkage to
zlib.
Merge pull request #132 from tamiko/fix_step53

Bugfix: step-53 requires enabled DEAL_II_WITH_ZLIB
Testsuite: Fix globbing command for all-headers tests, cleanup code

Turns out that globbing together a full path and manually extracting
relative paths is not the best idea. Clean up this mess by using
FILE(GLOB_RECURSE [base path] [...]) that produces nice relative paths.
Merge pull request #133 from tamiko/fix_header_tests

Bugfix: Fix all_header tests