Fixes #4323.

Before, customisation of DOCDIR did not lead to
changes of the EXAMPLE_CONF_DIR default value.
This was inconsistent with expected behaviour
if you didn't know of the existence of the
EXAMPLE_CONF_DIR variable. The confusion is
very strong, as (for not in place builds) both
DOCDIR and EXAMPLE_CONF_DIR share the same
default value, it is unexpected that setting
CUSTOM_DOCDIR changes the location of all
documentation files but one.

The best meaning of EXAMPLE_CONF_DIR is to
further allow customization of the mt.conf.example
storage place, but otherwise keep defaulting to
whatever DOCDIR is set to, at least for not in
place builds. This patch implements that
behaviour.

Fixes #3863.

Fix regression since commit:

915807f8 "Rename doc/mapformat.txt and update doc to match SRP changes"

And add an underscore to doc file name to make it more readable.

-Complies with the Linux standard freedesktop icon naming specs: http://standards.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html#guidelines
-Ensures compatibility with icon themes
-Edit minetest.desktop, CMakeLists.txt and README.md to reflect this change

This fixes the problem where 0.4.12-dev versions were erroneously shown as
0.4.11-dev because the tag was added on a separate branch.  It also fixes a
similar issue when builders didn't fetch new tags when updating.

This also removes the number-of-commits-since-tag field, since it's
incompatible with this.  Said field doesn't seem to be useful anyway if you
have the commit hash.

  * Combine client and server man pages.
  * Update unit test options and available databases in man page.
  * Add `--worldname` to man page.
  * Fix a bunch of places where `"Minetest"` was used directly instead of `PROJECT_NAME`.
  * Disable server build by default on all operating systems.
  * Make `ENABLE_FREETYPE` not fail if FreeType isn't found.
  * Enable LevelDB, Redis, and FreeType detection by default.
  * Remove the `VERSION_PATCH_ORIG` hack.
  * Add option to search for and use system JSONCPP.
  * Remove broken LuaJIT version detection.
  * Rename `DISABLE_LUAJIT` to `ENABLE_LUAJIT`.
  * Rename `minetest_*` variables in `version.{h,cpp}` to `g_*`.
  * Clean up style of CMake files.

Signed-off-by: Craig Robbins <kde.psych@gmail.com>

If CMake is run and Doxygen is found, add a make target called "doc",
which builds API documention in doc/html. This target is not included
in the default "all" target, you have to explicitly run "make doc" to
generate the documentation.

If graphviz is installed, in particular, if the "dot" binary is found,
doxygen is configured to generate various kinds of diagrams. Note that
due to this, the first run of doxygen can take a while.

Add ZLIBWAPI_DLL and LEVELDB_DLL CMake options Remove legacy MINGWM10_DLL CMake option Update 32-bit buildbot (OpenAL updated, zlib updated) Change build directory for buildbots to '_build' to prevent removal of Android build files Use -win64 suffix for 64-bit Windows builds Fixes #1476