util: Abort on failing CHECK_NONFATAL in debug builds

This requires adjusting some tests to force exceptions over aborts, or
accept either exceptions or aborts.

Also, remove a fuzz test in integer.cpp that is mostly redundant with
the unit test added in the prior commit.

test/functional/rpc_misc.py

@@ -15,6 +15,9 @@ from test_framework.util import (
 
 from test_framework.authproxy import JSONRPCException
 
+import http
+import subprocess
+
 
 class RpcMiscTest(BitcoinTestFramework):
     def set_test_params(self):
@@ -24,11 +27,22 @@ class RpcMiscTest(BitcoinTestFramework):
         node = self.nodes[0]
 
         self.log.info("test CHECK_NONFATAL")
-        assert_raises_rpc_error(
-            -1,
-            'Internal bug detected: request.params[9].get_str() != "trigger_internal_bug"',
-            lambda: node.echo(arg9='trigger_internal_bug'),
-        )
+        msg_internal_bug = 'request.params[9].get_str() != "trigger_internal_bug"'
+        self.restart_node(0)  # Required to flush the chainstate
+        try:
+            node.echo(arg9="trigger_internal_bug")
+            assert False  # Must hit one of the exceptions below
+        except (
+                subprocess.CalledProcessError,
+                http.client.CannotSendRequest,
+                http.client.RemoteDisconnected,
+        ):
+            self.log.info("Restart node after crash")
+            assert_equal(-6, node.process.wait(timeout=10))
+            self.start_node(0)
+        except JSONRPCException as e:
+            assert_equal(e.error["code"], -1)
+            assert f"Internal bug detected: {msg_internal_bug}" in e.error["message"]
 
         self.log.info("test getmemoryinfo")
         memory = node.getmemoryinfo()['locked']