Uint31 support.
Int31 literals in native compiler.
Had to split Nativelambda in two files because of Retroknowledge
dependencies.
Partial support for open terms in int31.
Full support for int31 values in native compiler.
Readback for int31 values from native compiler.
Machine arithmetic operations for native compiler.

This completes the port of the native compiler to retroknowledge.
However, some testing and optimizations are still to be done.
Int31 decompilation in native compiler was still partial. Now fixed.
Optimizing Int31 support in native compiler, by not tagging
applications of I31 constructor as lazy.
nanoPG: takeover keypress only when text view has focus
nanoPG: when the cursor moves, scroll to make it appear on screen
Removing handshake from Spawn. It used marshalling, which is bad for
non-ML applications. Control channel can be also ignored.
Fix name of some Int31 operations in native compiler.
Fix exponential behavior in native compiler with retroknowledge.
Adapt test-suite to -I is ML only
Adapt coq_makefile build rules to new -R -I semantic
Revert "Revert part of eba6b75 as coq_makefile ignores -I if it overlaps with -R. (Fix for Rocq/Rational.)"

This reverts commit 7d3ce4012a53b123dac95381bf46aac65f865d69.

Conflicts:
	CHANGES
Add another critical bug to the test-suite.

I have a fix, I'm reviewing it because there may be other bugs around.