* 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>

* use `pool.sks-keyservers.net` as keyserver as it's often more reliable
than `keyserver.ubuntu.com` as you can see with Google.
* put script to multiple lines
    * build out-of-source
    * use two CPUs
        * make seems to fail if $(nproc) is used unlike WeeChat. ZNC has
          same issue.
* mark build as failed if one job fails immediately without waiting for
all builds to finish.
    * this doesn't stop jobs that didn't finish before build was marked
    failed.