Ancient CMake versions required upper-case commands. Later command
names became case-insensitive. Now the preferred style is lower-case.

Run the following shell code:

cmake --help-command-list |
grep -v "cmake version" |
while read c; do
    echo 's/\b'"$(echo $c | tr '[:lower:]' '[:upper:]')"'\(\s*\)(/'"$c"'\1(/g'
done >convert.sed &&
git ls-files -z -- bootstrap '*.cmake' '*.cmake.in' '*CMakeLists.txt' |
egrep -z -v '^(Utilities/cm|Source/kwsys/)' |
xargs -0 sed -i -f convert.sed &&
rm convert.sed

Better CPack grouping.

This module is automatically checked out when OGS_BUILD_GUI=ON and the executable
gets packaged with the Data Explorer.

Tetgen source is hosted at https://github.com/ufz/tetgen.git

A minimal shapelib is now part of the repo. This means shapelib stuff
is always available. Just include "shape/shapefil.h" and link to "shp".

Searching for optional submodules has to be actively enabled by this
option. This prevents unexpected CMake errors when developers checked
out the submodules without their knowledge (as it happens e.g. with
the Windows GitHub app).

OGS_DONT_USE_OPTIONAL_SUBMODULES should be set to ON on Travis builds.

logog header files have to be included e.g. with logog/include/logog.hpp