fixed error if gettext is disabled

Fixed the problem of <=r548 clients fucking up maps on >=r549 servers. Also, already fucked up maps are now loaded correctly.

Get rid of the system-specific updatelocales.sh and introduce an
updatepo cmake rule. po files are also updated before creating the mo
files, and we now keep the .pot file (in the po/en directory). To
stabilize the po file creation, file contents are sorted by source
filename.

Update po files in the process.

The po file should not be named c55 if we're in ∆. But since it is not
exposed at installation time, we don't actually need its name to be
based on the project name at all, so just call it minetest.po

This unbreaks the Windows build which would otherwise have problems at
the jthread level.

When not running in place, check if the assumed data path in
../share/APPNAME exists. If it doesn't exist, fall back to ../data
instead. This allows the program to run successfully from the checkout
directory even without the run-in-place flag active.

german translation file
and bashscript to update translations

* liquid flow no longer does random things when transformed
* if a flowi
ng liquid node doesn't have a solid block as neighbor, its spread distan
ce is shortened by 1

Completely rewrote the liquid transformation. The algorithm now exclusively modifies the current node in one iteration. Another change is that MapNode.param2 now stores a bit that tells other nodes if a flowing liquid node flows downwards. This is accomplished by two masks on param2 for the "flow down" bit and the "liquid level" bits.

This will be the base of future improvements to the liquid flow. However, in the current state flowing liquid does not always disappear when cut off its source. Be aware that this branch is work in progress.