Adds everything needed for SRP (and everything works too),
but still deactivated, as protocol v25 init packets aren't final yet.
Can be activated by changing the LATEST_PROTOCOL_VERSION header to 25
inside networkprotocol.h.

Uses system provided libgmp if found, if not it falls back to mini-gmp.

Now matches function comment

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.

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.