Improve schematic file-saving interface
Add ability to create temporary test files

Fixes #2678

This simplifies NodeResolver logic and makes some interfaces cleaner.

- Add ability to explicitly reset NodeResolve state (useful for unittesting)
- Remove non-essential NodeResolve methods modifying state from INodeDefManager
- Add const qualifier to NodeDefManager and ContentFeatures serialize

Minor misc. NodeResolver cleanups
Prefix faux content type constants for testing with t_ to avoid
confusion or name collisions

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.

Added some new translations
Fixed some overlenght lines

Small improvement on clouds rendering performance

Fixes issue #2667

- Fix unintended negation of condition
- Remove line_of_sight 'optimization'

Make gamedef optional when constructing an ObjDefManager
Add note about object ownership

-> Round negative numbers correctly CMakeLists.txt
-> Link Json with the static run-time library

Make sure to include random unittests in android builds, too
Use SWAP() macro
Ensure that negative ranges are tested as well in random unittests

This reverts commit 3be9787e.

This fixes an issue with erroneous float-to-int rounding that resulted in
truncation toward 0, causing a biased distribution.

On calling clear_redistered_biomes the registered_biomes table is cleared
by creating a new empty table, but the pointer is not updated to point to
the new one. So after calling more register_biome, the registered_biome
table always contains 0 items, which is an error. Instead, the table is
cleared by removing all its items so the pointer (minetest.registered_*)
remains valid.

It isn't needed anymore, sending ICraftDefManager over the network has been obsoleted
by protocol version 7.

Fix style, refactor assert, use '"' instead of "\"",
replace code duplicating craftGetItemName, rename iterators.

Split unit tests into separate files under src/unittest/
Give better unittest diagnostics
Clean up some code